Add support for containerd cri registry config_path

[brandond]

Proposed Changes

Add support for containerd cri registry config_path

Render cri registry mirrors.x.endpoints and configs.x.tls into config_path; keep
using mirrors.x.rewrites and configs.x.auth those do not yet have an
equivalent in the new format.

The new config file format allows disabling containerd's fallback to the
default endpoint when using mirror endpoints; a new CLI flag is added to
control that behavior.

This also re-shares some code that was unnecessarily split into parallel
implementations for linux/windows versions. There is probably more work
to be done on this front but it's a good start.

• Requires new patch to containerd to extend rewrite support to hosts.toml:
  k3s-io/containerd@f4e0ac9
• Builds on:
  Bump containerd/runc to v1.7.10-k3s1/v1.1.10 #8962

Types of Changes

deprecated functionality

Verification

Confirm that registry mirrors, auth, and tls still work

Testing

Linked Issues

• Allow disabling containerd registry mirror default endpoint fallback #8975
• Containerd CRI registry mirrors and configs config via config.toml have been deprecated #8972
• Support for containerd 1.5+ config_path: On-the-fly container registry configuration #5568

User-Facing Change

Further Comments

[codecov]

Codecov Report

Attention: 75 lines in your changes are missing coverage. Please review.

Comparison is base (08ccea5) 41.56% compared to head (f4f7850) 41.43%.
Report is 1 commits behind head on master.

Files	Patch %	Lines
pkg/agent/containerd/config.go	18.66%	54 Missing and 7 partials ⚠️
pkg/agent/templates/templates.go	33.33%	9 Missing and 1 partial ⚠️
pkg/agent/templates/templates_linux.go	0.00%	3 Missing ⚠️
pkg/agent/containerd/config_linux.go	66.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8973      +/-   ##
==========================================
- Coverage   41.56%   41.43%   -0.13%     
==========================================
  Files         148      150       +2     
  Lines       15946    16024      +78     
==========================================
+ Hits         6628     6640      +12     
- Misses       8189     8250      +61     
- Partials     1129     1134       +5     

Flag	Coverage Δ
inttests	38.67% <24.24%> (-0.12%)	⬇️
unittests	18.19% <0.00%> (-0.16%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

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