Remove version_type "internal" from rest api specs

[russcam]

This commit removes the version_type "internal" from the rest api specs.
Support for internal versioning for optimistic concurrency control was
removed in #38254.

Since this removes values from rest api specs, it will affect any artifact that is generated from specs, for example, clients.

Other observations

• VersionType enum still has an INTERNAL value, which might be needed for bwc?
• SetProcessorTests randomly selects a version type which includes "internal" - this should probably also be removed.
• IngestServiceTests randomly selects a version type which includes "internal" and "external_gt" - these should probably also be removed.

[elasticmachine]

Pinging @elastic/es-distributed (Team:Distributed)

[elasticmachine]

Pinging @elastic/clients-team (Team:Clients)

[arteam]

@elasticmachine test this please

[arteam]

@elasticmachine update branch

[elasticmachine]

merge conflict between base and head

[arteam]

Hey @russcam! Could you please merge/rebase your changes? I think ClientYamlSuiteRestApiTests got moved to a different directory in 0ec2290

[russcam]

@arteam done

[arteam]

@elasticmachine test this please

[arteam]

@elasticmachine generate changelog

[arteam]

@elasticmachine test this please

[arteam]

Hey @russcam. Sorry for getting back to you late. Unfortunately, this change would qualify as a breaking change under the Elasticsearch guidelines. We try to avoid introducing breaking changes in Elasticsearch unless there is a considerable benefit in doing so. Currently, removing the "internal" version_type from the specs wouldn't be a considerable improvement for users who try to use it (they would get a runtime error), but it can break users who specify version_type: internal by accident or by using some older SDK versions. Thanks!