Add changelog for release v1.2.0-rc1 (#3327)

* Add changelog for release v1.2.0-rc1

Signed-off-by: Nick Young <[email protected]>

* Fix changelog PR comments and generate new files

Also updates the update-codegen script to work
on M3 Macs inside a Linux VM.

Signed-off-by: Nick Young <[email protected]>

* Updating v1.2 changelog to cover k8s dep updates and gwctl move

* Call out breaking SupportedFeatures change

Signed-off-by: Nick Young <[email protected]>

---------

Signed-off-by: Nick Young <[email protected]>
Co-authored-by: Rob Scott <[email protected]>

Author: youngnick

CHANGELOG/1.2-CHANGELOG.md

@@ -0,0 +1,13 @@
+# v1.2 Release Team
+
+| Enhancement | Leads |
+| - | - |
+| Infrastructure Labels and Annotations | @keithmattix, @snorwin |
+| HTTPRoute Timeouts and Durations | @kflynn, @xtineskim |
+| BackendProtocol Support | @dprotaso |
+| HTTPRoute Retries | @mikemorris |
+| Percentage-based request mirroring | @jakebennert |
+| Backend TLS Config improvments | @mkosieradzki, @LiorLieberman |
+| Named Route Rules | @guicassolato, @howardjohn |
+| Conformance Profiles and Reports | @mlavacca, @shaneutt, @xtineskim |
+| Gateway API Maintainers | @mlavacca, @robscott, @shaneutt, @youngnick  |