add kstem token filter docs #8150 (#8473)

* add kstem token filter docs #8150

Signed-off-by: Anton Rubin <[email protected]>

* Doc review

Signed-off-by: Fanit Kolchina <[email protected]>

* Apply suggestions from code review

Co-authored-by: Nathan Bower <[email protected]>
Signed-off-by: kolchfa-aws <[email protected]>

---------

Signed-off-by: Anton Rubin <[email protected]>
Signed-off-by: Fanit Kolchina <[email protected]>
Signed-off-by: kolchfa-aws <[email protected]>
Co-authored-by: Fanit Kolchina <[email protected]>
Co-authored-by: kolchfa-aws <[email protected]>
Co-authored-by: Nathan Bower <[email protected]>
(cherry picked from commit ac852d6)
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

_analyzers/token-filters/index.md

@@ -36,7 +36,7 @@ Token filter | Underlying Lucene token filter|  Description
 [`keep_words`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/keep-words/)  | [KeepWordFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/miscellaneous/KeepWordFilter.html) | Checks the tokens against the specified word list and keeps only those that are in the list.
 [`keyword_marker`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/keyword-marker/)  | [KeywordMarkerFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/miscellaneous/KeywordMarkerFilter.html) | Marks specified tokens as keywords, preventing them from being stemmed.
 `keyword_repeat` | [KeywordRepeatFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/miscellaneous/KeywordRepeatFilter.html) | Emits each incoming token twice: once as a keyword and once as a non-keyword.
-`kstem` | [KStemFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/en/KStemFilter.html) | Provides kstem-based stemming for the English language. Combines algorithmic stemming with a built-in dictionary.
+[`kstem`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/kstem/) | [KStemFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/en/KStemFilter.html) | Provides KStem-based stemming for the English language. Combines algorithmic stemming with a built-in dictionary.
 `kuromoji_completion` | [JapaneseCompletionFilter](https://lucene.apache.org/core/9_10_0/analysis/kuromoji/org/apache/lucene/analysis/ja/JapaneseCompletionFilter.html) | Adds Japanese romanized terms to the token stream (in addition to the original tokens). Usually used to support autocomplete on Japanese search terms. Note that the filter has a `mode` parameter, which should be set to `index` when used in an index analyzer and `query` when used in a search analyzer. Requires the `analysis-kuromoji` plugin. For information about installing the plugin, see [Additional plugins]({{site.url}}{{site.baseurl}}/install-and-configure/plugins/#additional-plugins).
 [`length`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/length/) | [LengthFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/miscellaneous/LengthFilter.html) | Removes tokens that are shorter or longer than the length range specified by `min` and `max`. 
 [`limit`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/limit/) | [LimitTokenCountFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/miscellaneous/LimitTokenCountFilter.html) | Limits the number of output tokens. For example, document field value sizes can be limited based on the token count.

_analyzers/token-filters/kstem.md

@@ -0,0 +1,92 @@
+---
+layout: default
+title: KStem
+parent: Token filters
+nav_order: 220
+---
+
+# KStem token filter
+
+The `kstem` token filter is a stemming filter used to reduce words to their root forms. The filter is a lightweight algorithmic stemmer designed for the English language that performs the following stemming operations:
+
+- Reduces plurals to their singular form.
+- Converts different verb tenses to their base form.
+- Removes common derivational endings, such as "-ing" or "-ed".
+
+The `kstem` token filter is equivalent to the a `stemmer` filter configured with a `light_english` language. It provides a more conservative stemming compared to other stemming filters like `porter_stem`.
+
+The `kstem` token filter is based on the Lucene KStemFilter. For more information, see the [Lucene documentation](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/en/KStemFilter.html).
+
+## Example
+
+The following example request creates a new index named `my_kstem_index` and configures an analyzer with a `kstem` filter:
+
+```json
+PUT /my_kstem_index
+{
+  "settings": {
+    "analysis": {
+      "filter": {
+        "kstem_filter": {
+          "type": "kstem"
+        }
+      },
+      "analyzer": {
+        "my_kstem_analyzer": {
+          "type": "custom",
+          "tokenizer": "standard",
+          "filter": [
+            "lowercase",
+            "kstem_filter"
+          ]
+        }
+      }
+    }
+  },
+  "mappings": {
+    "properties": {
+      "content": {
+        "type": "text",
+        "analyzer": "my_kstem_analyzer"
+      }
+    }
+  }
+}
+```
+{% include copy-curl.html %}
+
+## Generated tokens
+
+Use the following request to examine the tokens generated using the analyzer:
+
+```json
+POST /my_kstem_index/_analyze
+{
+  "analyzer": "my_kstem_analyzer",
+  "text": "stops stopped"
+}
+```
+{% include copy-curl.html %}
+
+The response contains the generated tokens:
+
+```json
+{
+  "tokens": [
+    {
+      "token": "stop",
+      "start_offset": 0,
+      "end_offset": 5,
+      "type": "<ALPHANUM>",
+      "position": 0
+    },
+    {
+      "token": "stop",
+      "start_offset": 6,
+      "end_offset": 13,
+      "type": "<ALPHANUM>",
+      "position": 1
+    }
+  ]
+}
+```