[Source Versioning] SS-60 update docs for SQL server source versioning

[patrickwwbutler]

Updates docs describing process to add/remove columns from SQL Server upstream sources

Motivation

• This PR adds a known-desirable feature.
  https://linear.app/materializeinc/issue/SS-60/write-docs-for-sql-server-source-versioning

Checklist

• This PR has adequate test coverage / QA involvement has been duly considered. (trigger-ci for additional test/nightly runs)
• This PR has an associated up-to-date design doc, is a design doc (template), or is sufficiently small to not require a design.
• If this PR evolves an existing $T ⇔ Proto$T mapping (possibly in a backwards-incompatible way), then it is tagged with a T-proto label.
• If this PR will require changes to cloud orchestration or tests, there is a companion cloud PR to account for those changes that is tagged with the release-blocker label (example).
• If this PR includes major user-facing behavior changes, I have pinged the relevant PM to schedule a changelog post.

[martykulma]

Should also update the SQL pages for CREATE SOURCE and CREATE TABLE to include SQL Server.