[Protobuf-Schema] Add unknown to enum switch

[Yurzel]

resolves #10891

Codegen

• New "startEnumsWithUnknown" switch (default is false)

[wing328]

Thanks for the PR but your commit (as shown in the Commits tab) is not linked to your Github account, which means this PR won't count as your contribution in https://github.com/OpenAPITools/openapi-generator/graphs/contributors.

Let me know if you need help fixing it.

Ref: https://github.com/OpenAPITools/openapi-generator/wiki/FAQ#how-can-i-update-commits-that-are-not-linked-to-my-github-account

[wing328]

I just merge another PR submitted by you. Can you please resolve the merge conflicts in this PR when you've time?

[Yurzel]

Done.

I forgot to generate docs, so thats done aswell. The last PR will have conflicts aswell, so I'll fix that one too when you merge this.