Add detailed versioning docs for single preview

[markcowl]

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[azure-sdk]

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[azure-sdk]

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[haolingdong-msft]

Thank you @markcowl for putting the versioning related documents together in this PR. It is really helpful and I've learnt a lot! left some comments for understanding and clarification purpose. Thank you so much for your guidance!

May I also ask two general questions?

1. I saw there is also a versioning doc here: https://azure.github.io/typespec-azure/docs/howtos/versioning/preview-version/. Is this for data-plane? (Basically two versioning related documents in the typespec azure website, so I'm just a bit confused)

2. Does this PR include information in below two docs about versioning you've shared before? From my understanding, it includes, but just would like to confirm.

Rules for Versioning Decorators.loop
Scenarios for API Evolution.loop

[markcowl]

Thank you @markcowl for putting the versioning related documents together in this PR. It is really helpful and I've learnt a lot! left some comments for understanding and clarification purpose. Thank you so much for your guidance!

May I also ask two general questions?

1. I saw there is also a versioning doc here: https://azure.github.io/typespec-azure/docs/howtos/versioning/preview-version/. Is this for data-plane? (Basically two versioning related documents in the typespec azure website, so I'm just a bit confused)

2. Does this PR include information in below two docs about versioning you've shared before? From my understanding, it includes, but just would like to confirm.
Rules for Versioning Decorators.loop Scenarios for API Evolution.loop

Yeah, one really important thing is that we make this documentation visible for those who need to see it. I think we might rename the existing doc to 'indicate that it is for 'data-plane only' and introduce another doc alongside it that is for arm, with links to the rest of this documentation.

[qiaozha]

Haven't read all of them yet.

[qiaozha]

To summarize the main different opinion, I have here is:

1. we can have a vlatestPreview enum key for latest preview versions in the Versions enum.
2. we can change the mechanism of version continuity of all versioning decorators for preview versions to not extend to stable. It can be extended to newer preview but that was because we have move forward the vlatestPreview value in the version enum. But we can keep the version continuity of all versioning decorators for stable versions.

So that if any feature/changes are still in preview, it has to have the according versioning decorators with a vlatestPreview enum member in it. TypeSpec authors can just focus on the changes happened after it gets GA.