feat: Populate cluster cache info in principal

[jparsai]

This PR is to add logic to populate cluster cache info in principal from managed agent. The agent will also send periodic events to principal to keep it updated about any changes in managed cluster cache. The principal will receive and update the control-plane cache. The UI running on control-plane will read the info and display it along with other details.

Fixes: #418

[codecov-commenter]

Codecov Report

❌ Patch coverage is 59.27835% with 79 lines in your changes missing coverage. Please review.
✅ Project coverage is 45.10%. Comparing base (edfedbd) to head (d789bf0).

Files with missing lines	Patch %	Lines
internal/argocd/cluster/cluster.go	73.17%	15 Missing and 7 partials ⚠️
agent/agent.go	23.52%	12 Missing and 1 partial ⚠️
internal/event/event.go	0.00%	13 Missing ⚠️
agent/outbound.go	75.75%	6 Missing and 2 partials ⚠️
cmd/argocd-agent/agent.go	0.00%	7 Missing ⚠️
internal/argocd/cluster/manager.go	41.66%	6 Missing and 1 partial ⚠️
agent/options.go	0.00%	5 Missing ⚠️
internal/manager/application/application.go	0.00%	2 Missing ⚠️
principal/event.go	89.47%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #513      +/-   ##
==========================================
+ Coverage   44.86%   45.10%   +0.24%     
==========================================
  Files          88       88              
  Lines       10795    10945     +150     
==========================================
+ Hits         4843     4937      +94     
- Misses       5565     5618      +53     
- Partials      387      390       +3     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[jgwest]

LGTM, thanks @jparsai!