[v2] RPCV2 CBOR Protocol Support

[aemous]

Description of changes:

• Adds support for RPCV2 parsing and serialization. Includes updates to relevant tests, e.g. protocol tests.
• The following (already approved) PRs are included in this PR. No other changes are included:
  • Rpcv2 protocol parser #9367
  • Rpcv2 protocol serializer #9381

Description of tests:

• Ran all CI and test suites
• No further testing can be justified since wire-level parsing & serialization is hidden from the AWS CLI v2.

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[AndrewAsseily]

Lgtm! Approved with just one small formatting suggestion.