Fix additional corner cases in registries handling

[brandond]

Proposed Changes

Fix additional corner cases in registries handling

• Add support for explicit default endpoint (default endpoint address manually included in last position in endpoint list)
• Add support for loading tls and credential config from wildcard entry.

Types of Changes

bugfix

Verification

See linked issue

Testing

yes

Linked Issues

• Fix remaining corner cases in containerd certs.d support #9341
• internal-ref: SURE-7640

User-Facing Change

Further Comments

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 13 lines in your changes are missing coverage. Please review.

Project coverage is 42.99%. Comparing base (fae0d99) to head (9964bef).

Files	Patch %	Lines
pkg/agent/containerd/config.go	80.00%	8 Missing and 5 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9556      +/-   ##
==========================================
- Coverage   49.19%   42.99%   -6.20%     
==========================================
  Files         151      154       +3     
  Lines       13471    13541      +70     
==========================================
- Hits         6627     5822     -805     
- Misses       5506     6549    +1043     
+ Partials     1338     1170     -168     

Flag	Coverage Δ
e2etests	?
inttests	39.42% <0.00%> (-0.08%)	⬇️
unittests	16.18% <80.00%> (?)

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