[FEATURE] Generate API code from OpenSearch API Spec

[Xtansia]

Is your feature request related to a problem?

Related to opensearch-project/opensearch-clients#19

What solution would you like?

Re-use the generator that generates API Code that maintains backwards compatibility with the current client APIs and provides a way to add new APIs.

Old generator was cleaned up in 7db02e9 so will need reverting and modification.

What alternatives have you considered?

Using OpenAPI generators instead of re-using the existing generator but it makes it difficult to maintain backwards compatibility.

Do you have any additional context?

Add any other context or screenshots about the feature request here.

[dblock]

@Xtansia Can we close this?

[Xtansia]

@dblock Splitting remaining work into new issues and closing this one:

• [FEATURE] Automate running of the API generator #667
• [FEATURE] Extend API generation to generate request/response bodies #668
• [FEATURE] Regenerate remaining previously generated namespaces #669
• [FEATURE] Generate newly added APIs and plugins #670