fix(konnect): update nodes status only when it actually changes

[czeslavo]

What this PR does / why we need it:

Makes sure that:

• NodeAgent calls Konnect APIs only when the config status actually changes (enforce that on both ends of the notification channel - in NodeAgent and in KongClient). This was an actual reason for KIC updating nodes every 3s.
• NodeAgent calls Konnect APIs only when a set of Gateway clients actually changes (enforce that on ClientsManager side)

Also improves debug logging to make it visible when the calls are made.

After this change, NodeAgent will call Konnect APIs in the following cases:

• configuration status has changed,
• gateways' clients have changed (Gateway deployment scaling, Pod eviction, etc.),
• every 30s.

Which issue this PR fixes:

Fixes #4322.

PR Readiness Checklist:

Complete these before marking the PR as ready to review:

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

[codecov]

Codecov Report

Patch coverage: 94.8% and project coverage change: +0.1 🎉

Comparison is base (c8843de) 64.9% compared to head (0be0a59) 65.1%.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #4324     +/-   ##
=======================================
+ Coverage   64.9%   65.1%   +0.1%     
=======================================
  Files        154     154             
  Lines      17384   17416     +32     
=======================================
+ Hits       11297   11339     +42     
+ Misses      5367    5356     -11     
- Partials     720     721      +1     

Impacted Files	Coverage Δ
internal/konnect/node_agent.go	61.0% <91.4%> (+3.5%)	⬆️
internal/clients/manager.go	94.7% <100.0%> (+0.1%)	⬆️
internal/dataplane/kong_client.go	85.1% <100.0%> (+0.3%)	⬆️

... and 4 files with indirect coverage changes

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[pmalek]

👍 Some minor comments to consider

[pmalek]

I believe the milestone should be set to v2.11, right? The backport will have it set to v2.10.

[github-actions]

The backport to release/2.10.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/2.10.x release/2.10.x
# Navigate to the new working tree
cd .worktrees/backport-release/2.10.x
# Create a new branch
git switch --create backport-4324-to-release/2.10.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 f861118a88b9e67aa37cd42edda0162d184026e4
# Push it to GitHub
git push --set-upstream origin backport-4324-to-release/2.10.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-release/2.10.x

Then, create a pull request where the base branch is release/2.10.x and the compare/head branch is backport-4324-to-release/2.10.x.