[v2] Add protocols trait support

[aemous]

This is a port of boto/botocore#3376 to our vendored botocore.

Description of changes:

• Add support for protocols trait on service models.
• Selects the highest priority supported protocol.
• Falls back to legacy protocol trait if service model does not define protocols trait.

Description of tests:

• Ran and passed all tests (unit, functional, integration, etc.)
• No further CLI-specific tests are needed because the CLI is protocol-agnostic; protocol behavior is fully contained within botocore.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 0.00%. Comparing base (d413154) to head (9d983ee).
Report is 43 commits behind head on v2.

Additional details and impacted files

@@    Coverage Diff     @@
##   v2   #9291   +/-   ##
==========================
==========================

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.