feat: Live resource view

[jannfis]

What does this PR do / why we need it:

This PR introduces functionality to provide live resource view from the agents to the control plane. There are still a few caveats with this, and some things to sort out.

The general architecture is documented here.

It's also the pre-requisite for other upcoming features, such as log view, resource actions and resource manipulation, this is why I'd like to have the code in early.

The CLI components to manipulate cluster secrets will be a follow-up PR.

Which issue(s) this PR fixes:

Fixes #?

How to test changes / Special notes to the reviewer:

The CLI code for managing cluster secrets will be submitted in a different PR, thus, the code in here is potentially difficult to test.

Checklist

• Documentation update is required by this PR (and has been updated) OR no documentation update is required.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 46.45914% with 688 lines in your changes missing coverage. Please review.

Project coverage is 48.22%. Comparing base (d16afb3) to head (aac6a5e).

Files with missing lines	Patch %	Lines
cmd/principal/main.go	0.00%	93 Missing ⚠️
principal/server.go	14.94%	68 Missing and 6 partials ⚠️
agent/inbound.go	10.25%	70 Missing ⚠️
cmd/cmdutil/log.go	0.00%	51 Missing ⚠️
internal/event/event.go	7.54%	49 Missing ⚠️
internal/argocd/cluster/informer.go	58.82%	26 Missing and 9 partials ⚠️
internal/resourceproxy/resourceproxy.go	72.00%	27 Missing and 8 partials ⚠️
principal/resource.go	70.17%	27 Missing and 7 partials ⚠️
internal/argocd/cluster/conversion.go	42.30%	18 Missing and 12 partials ⚠️
cmd/cmdutil/term.go	0.00%	24 Missing ⚠️
... and 18 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #267      +/-   ##
==========================================
+ Coverage   48.20%   48.22%   +0.02%     
==========================================
  Files          55       73      +18     
  Lines        5066     6268    +1202     
==========================================
+ Hits         2442     3023     +581     
- Misses       2424     2986     +562     
- Partials      200      259      +59     

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