Deduplicate configuration subscriptions

[alcarney]

Expected behavior

Subscriptions to identical configuration values be de-duplicated.

Actual behavior

Subscriptions to identical configuration values are duplicated.
While not necessarily a problem, it does lead to a lot of noise in the debug logs...

Log output

[esbonio.Configuration] ConfigurationContext(file_scope='', workspace_scope='')
[esbonio.Configuration] esbonio.server.completion: {
  "preferredInsertBehavior": "replace"
}
[esbonio.Configuration] CompletionConfig(preferred_insert_behavior='replace')
[esbonio.Configuration] Previous: CompletionConfig(preferred_insert_behavior='replace')
[esbonio.Configuration] Current: CompletionConfig(preferred_insert_behavior='replace')
[esbonio.Configuration] ConfigurationContext(file_scope='', workspace_scope='')
[esbonio.Configuration] esbonio.server.completion: {
  "preferredInsertBehavior": "replace"
}
[esbonio.Configuration] CompletionConfig(preferred_insert_behavior='replace')
[esbonio.Configuration] Previous: CompletionConfig(preferred_insert_behavior='replace')
[esbonio.Configuration] Current: CompletionConfig(preferred_insert_behavior='replace')
[esbonio.Configuration] ConfigurationContext(file_scope='', workspace_scope='')
[esbonio.Configuration] esbonio.server.completion: {
  "preferredInsertBehavior": "replace"
}
[esbonio.Configuration] CompletionConfig(preferred_insert_behavior='replace')
[esbonio.Configuration] Previous: CompletionConfig(preferred_insert_behavior='replace')
[esbonio.Configuration] Current: CompletionConfig(preferred_insert_behavior='replace')
[esbonio.Configuration] ConfigurationContext(file_scope='', workspace_scope='')
[esbonio.Configuration] esbonio.server.completion: {
  "preferredInsertBehavior": "replace"
}
[esbonio.Configuration] CompletionConfig(preferred_insert_behavior='replace')
[esbonio.Configuration] Previous: CompletionConfig(preferred_insert_behavior='replace')
[esbonio.Configuration] Current: CompletionConfig(preferred_insert_behavior='replace')

(Optional) Settings from conf.py

No response