Update CHANGELOG with v1.2.0-rc2 details (#3363)

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

Author: youngnick

CHANGELOG/1.2-CHANGELOG.md

@@ -2,8 +2,44 @@
 
 ## Table of Contents
 
+- [v1.2.0-rc2](#v120-rc2)
 - [v1.2.0-rc1](#v120-rc1)
 
+# v1.2.0-rc2
+
+This release candidate should be the same as the final v1.2.0 release.
+
+This release candidate is suitable for implementors, but we do not recommend
+shipping products based on a release candidate API due to the possibility of
+incompatible changes prior to the final release. The following represents the
+changes since v1.2.0-rc1:
+
+## Breaking Changes
+
+### `GRPCRoute` and `ReferenceGrant` `v1alpha2` removal
+
+As per a previous deprecation notice, in this version, both Experimental
+and Standard channel YAMLs will no longer serve the `v1alpha2` versions
+of `GRPCRoute` and `ReferenceGrant`.
+
+For the final release, we will provide pre-upgrade migration instructions
+to cover folks who have been using the `v1alpha2` versions of these objects.
+
+* Disable v1alpha2 versions for GRPCRoute and ReferenceGrant by @youngnick in
+  [#3361](https://github.com/kubernetes-sigs/gateway-api/pull/3361)
+
+## Documentation Changes
+
+* Fix a number of GEP stage errors by @youngnick in
+  [#3359](https://github.com/kubernetes-sigs/gateway-api/pull/3359)
+
+## Testing and Conformance changes
+
+* Add conformance suite client options by @BobyMCbobs in 
+  [#3343](https://github.com/kubernetes-sigs/gateway-api/pull/3343)
+* Fix conformance test race condition by @caboteria in
+  [#3350](https://github.com/kubernetes-sigs/gateway-api/pull/3350)
+
 # v1.2.0-rc1
 
 We expect that this release candidate is quite close to the final v1.2.0