[PROPOSAL] Require the OpenAPI spec to be re-generated for pull requests

[dblock]

What/Why

What are you proposing?

With the addition of coverage in #179 I propose we move the build into PRs as well.

1. Make ./gradlew build output/overwrite OpenSearch.openapi.json at the root.
2. Make CI fail if that file is not up-to-date.

What problems are you trying to solve?

Currently CI/CD re-generates the OpenAPI spec and makes a PR. This causes several issues.

• Warnings are ignored, whereas they should be errors (see [PROPOSAL] Turn warnings into errors #184).
• Coverage can't know what has changed next to the actual API spec change.
• We have 2 commits for every PR.

What is the developer experience going to be?

Require that developers run ./gradlew build before a PR can be merged.

[nhtruong]

@dblock will #211 resolve this one as well?

[dblock]

Yes, closing.