add bug report and feature request template

.github/ISSUE_TEMPLATE/bug_report.yaml

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+name: Bug Report
+description: Report a bug on Marsilea
+title: "[BUG]: "
+labels: ["bug", "triage"]
+assignees:
+  - Mr-Milk
+body:
+  - type: textarea
+    id: summary
+    attributes:
+      label: Describe the bug
+      description: Describe what the bug is in 1-2 short sentences.
+    validations:
+      required: true
+  - type: textarea
+    id: reproduction
+    attributes:
+      label: Code for reproduction
+      description: >-
+        If possible, please provide a minimum self-contained example. You can use synthetic datasets.
+      placeholder: Paste your code here. This field is automatically formatted as Python code.
+      render: Python
+    validations:
+      required: true
+  - type: textarea
+    id: actual
+    attributes:
+      label: Actual outcome
+      description: >-
+        Paste the output produced by the code provided above, e.g.
+        console output, images/videos produced by the code, any relevant screenshots/screencasts, etc.
+    validations:
+      required: true
+  - type: textarea
+    id: expected
+    attributes:
+      label: Expected outcome
+      description: Describe (or provide a visual example of) the expected outcome from the code snippet.
+    validations:
+      required: true
+  - type: textarea
+    id: details
+    attributes:
+      label: Additional information
+      description: |
+        - What are the conditions under which this bug happens? input parameters, edge cases, etc?
+        - Has this worked in earlier versions?
+        - Do you know why this bug is happening?
+        - Do you maybe even know a fix?
+  - type: input
+    id: marsilea-version
+    attributes:
+      label: Marsilea Version
+      description: "From Python prompt: `import marsilea; print(marsilea.__version__)`"
+    validations:
+      required: true

.github/ISSUE_TEMPLATE/feature_request.yaml

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+---
+name: Feature Request
+description: Suggest something new or missing to Marsilea!
+title: "[NEW FEATURE]: "
+labels: [New feature]
+body:
+  - type: markdown
+    attributes:
+      value: >-
+        Please search the [issues](https://github.com/matplotlib/matplotlib/issues) for relevant feature
+        requests before creating a new feature request.
+  - type: textarea
+    id: problem
+    attributes:
+      label: Problem/New Plotter
+      description: Briefly describe the problem this feature will solve. (2-4 sentences)
+      placeholder: |
+        * I'm always frustrated when [...] because [...]
+        * I would like it if [...] happened when I [...] because [...]
+        * Here is a sample image of what I am asking for [...]
+    validations:
+      required: true
+  - type: textarea
+    id: solution
+    attributes:
+      label: Proposed solution
+      description: Describe a way to accomplish the goals of this feature request.