Inspect loadbalancer address from Envoy ingress objects

[tsaarni]

This PR is continuation of #5987 by @hligit and @kahirokunn.

Contour propagates load balancer addresses to Ingress/HTTPProxy status. Currently the address source is always a Service. This PR adds a --load-balancer-status flag that unifies address source configuration:

• address:<addr,...>: static addresses (IP or FQDN)
• service:<namespace>/<name>: watch a Service's LoadBalancer status
• ingress:<namespace>/<name>: watch an Ingress object's LoadBalancer status (new)

Also available as spec.envoy.loadBalancer in ContourConfiguration CRD or load-balancer-status in config file.

Changes compared to #5987:

• Renamed hostname: kind to address: to support both IP and FQDN
• Updated docs and error messages
• Refactored tests
• Stop initializing Service watcher unconditionally, to avoid it fighting with the Ingress watcher

TODO

• Create new specific types for CRD and config file: (1) namespaced service name ref, (2) namespaced ingress name ref and (3) list of addresses. This is the way how we have handled all existing fields as well and we had no precedence of using single string to multiplex resource references, so I think we should use <kind>:<value> only for --load-balancer-status flag (or simply not support CLI option for ingress at all)
• Untangle how different load balancer status source parameters are passed around internally to reduce duplication and confusion

Fixes #4952

[codecov]

Codecov Report

❌ Patch coverage is 45.86466% with 72 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.14%. Comparing base (a172ab8) to head (eb0780c).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/contour/serve.go	29.41%	60 Missing ⚠️
internal/k8s/statusaddress.go	76.08%	7 Missing and 4 partials ⚠️
cmd/contour/ingressstatus.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7595      +/-   ##
==========================================
- Coverage   82.35%   82.14%   -0.22%     
==========================================
  Files         130      130              
  Lines       15873    15994     +121     
==========================================
+ Hits        13073    13138      +65     
- Misses       2513     2566      +53     
- Partials      287      290       +3     

Files with missing lines	Coverage Δ
cmd/contour/servecontext.go	86.60% <100.00%> (+0.03%)	⬆️
pkg/config/parameters.go	87.10% <ø> (ø)
cmd/contour/ingressstatus.go	26.96% <0.00%> (ø)
internal/k8s/statusaddress.go	80.54% <76.08%> (-1.48%)	⬇️
cmd/contour/serve.go	25.00% <29.41%> (+0.98%)	⬆️

... and 1 file with indirect coverage changes

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[tsaarni]

I am marking this PR as a draft because there is more work to do than I initially anticipated.