Uninstall/uninitialized an extension

[dblock]

Is your feature request related to a problem? Please describe.

The extensions feature lets me initialize an extension, but doesn't support removing it and currently requires a restart of OpenSearch.

Describe the solution you'd like

One of these:

curl -XPOST "localhost:9200/_extensions/uninitialize" -H "Content-Type:application/json" --data @samples/hello/hello.json
curl -DELETE "localhost:9200/_extensions/_hello-world"

Additional context

Coming from opensearch-project/opensearch-sdk-py#43

[dbwiddis]

There is currently no way to uninstall an extension. The main blocker is #6395

See also opensearch-project/opensearch-sdk-java#356

There may be a way to “reconnect” to a previously installed extension as a workaround.