Rename Teams AI to Teams SDK 🎉

[corinagum]

[DO NOT MERGE BEFORE ALL PREVIOUS PRS ARE MERGED]

Renames 'Teams AI' to 'Teams SDK' comprehensively throughout this repo. This includes documentation, comments, and code snippets.

• Change references to Teams AI to Teams SDK
• Limit use of "Teams Library" in favor of "Teams SDK". Some uses of the word library were kept in cases of clarity, or when not referencing this SDK (e.g. MSAL)
• Limit use of 'v2' throughout the repo. Exceptions being root README.md for v1/v2 findability, migrations documentation, and in the few instances where differentiation of the two was still needed.
• Announcement bar set in docs, announcement set in root README.md

The rename does NOT include (for now):

• references to the GitHub repo itself, including the monorepo's package name
• github.io / base-url reference
• URL links that already use teams-ai
• package name references

This exceptions will be resolved at the same time that the rename of the GitHub repo itself occurs. TBD if it will be in this PR or a different one.