fix(fallback): do not skip config update when gateways out of sync

[czeslavo]

What this PR does / why we need it:

We didn't take into account that when new gateways are discovered, we need to make sure they're all populated with the current configuration. We cannot skip config updates based only on the Kubernetes config cache not changing - we also need to ensure all the gateways are populated using it.

Which issue this PR fixes:

Fixes https://github.com/Kong/kubernetes-ingress-controller/issues/6219.

PR Readiness Checklist:

Complete these before marking the PR as ready to review:

• [x] the CHANGELOG.md release notes have been updated to reflect any significant (and particularly user-facing) changes introduced by this PR

[team-k8s-bot]

The backport to release/3.2.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-release/3.2.x release/3.2.x
# Navigate to the new working tree
cd .worktrees/backport-release/3.2.x
# Create a new branch
git switch --create backport-6271-to-release/3.2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 3b547a9feaba331763601cb87612480cf515f850
# Push it to GitHub
git push --set-upstream origin backport-6271-to-release/3.2.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-release/3.2.x

Then, create a pull request where the base branch is release/3.2.x and the compare/head branch is backport-6271-to-release/3.2.x.