Add schema_version to notes

What does this MR do and why?

This MR adds an integer field schema_version in the notes mapping. This field is useful in the case of reindexing all documents of notes

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Before	After

How to set up and validate locally

1. Ensure Elasticsearch is enabled
2. Run the following command and ensure the mappings in the response is empty

curl -H 'Content-type: application/json' -XGET 'http://localhost:9200/gitlab-development-notes/_mapping/field/schema_version'

3. Now open the rails console

bundle exec rails c

4. Run the following command in the console

Elastic::DataMigrationService[20230824114205].send(:migration).migrate

5. Now again run the curl command in the bash terminal and ensure the mapping in the response has the values.
6. Now edit or create any note(comment) and check that note in the elastic. Verify that the schema_version field is populated.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #372856 (closed)

#384596 (closed)