Fix: Add MembersReferenceResolved condition for cp groups

[randmonkey]

What this PR does / why we need it:
Add a MembersReferenceResolved condition in status of control plane groups.
Which issue this PR fixes

Fixes #797

Special notes for your reviewer:

PR Readiness Checklist:

Complete these before marking the PR as ready to review:

• the CHANGELOG.md release notes have been updated to reflect significant changes

[pmalek]

Can we please cover this with a test? Perhaps we can extend the test cases in https://github.com/Kong/gateway-operator/blob/5d0b4b78c138f606b1eb5116e2649f35cf780bdb/test/envtest/konnect_entities_gatewaycontrolplane_test.go

[randmonkey]

Can we please cover this with a test? Perhaps we can extend the test cases in https://github.com/Kong/gateway-operator/blob/5d0b4b78c138f606b1eb5116e2649f35cf780bdb/test/envtest/konnect_entities_gatewaycontrolplane_test.go

Added unit tests.

[pmalek]

I'm doing some testing on this one and I do not see the condition set consistently. Let's put this on pause until that's resolved.

[pmalek]

This PR is missing setting the condition when we encounter a conflict against the API. Specifically when we hit

gateway-operator/controller/konnect/ops/ops.go

Line 118 in 170469a

id, err = getControlPlaneForUID(ctx, sdk.GetControlPlaneSDK(), ent)

we have to handle the members there as well (or requeue for update which will handle that, but that's only going to happen when the sync period passes).

[randmonkey]

This PR is missing setting the condition when we encounter a conflict against the API. Specifically when we hit

gateway-operator/controller/konnect/ops/ops.go

Line 118 in 170469a

id, err = getControlPlaneForUID(ctx, sdk.GetControlPlaneSDK(), ent)

we have to handle the members there as well (or requeue for update which will handle that, but that's only going to happen when the sync period passes).

Added setGroupMembers in getControlPlaneForUID.

[pmalek]

Please resolve conflicts that arose since last review.

Overall this looks good. Just 1 nit about adding a test case for this.