Release notes v2.2.0 (#6242)

* Add v2.2.0 release notes

* Add initial changes for release v2.2.0

* Apply suggestions from code review

Co-authored-by: Ankur <akahank@gmail.com>

* Update v2.2.0 release notes

Replace the template with the drafted notes covering
all 73 PRs merged between v2.1.0 and the release
branch tip.

* Update v2.2.0 release notes

Move the feature-flag PR links onto their bullets and
recategorize #5631 as an enhancement, covering the
headerValues() and browser traffic metric changes.

* Apply suggestions from code review

Co-authored-by: Ankur <akahank@gmail.com>

* Update v2.2.0 release notes

Group the renovate dependency bumps into Go, Docker,
and GitHub Actions lines, and squash the cloud API
cleanup and provisioning follow-up entries.

* Update v2.2.0 release notes

Cover the newly merged dependency bumps: grpc lands on
v1.83.0 and go-httpbin joins the grouped Go deps line.