api: support hot reload of registry authentication

[imeoer]

Overview

Add HTTP API endpoints to update and query daemon configuration at
runtime without restarting nydusd. This is particularly useful for
refreshing registry credentials when tokens expire.

Key changes:

• Add GET/PUT /api/v1/config endpoints for configuration management
• Add config module in utils for centralized configuration updates
• Add smoke test cases for hot reload configuration API
• Update documentation with hot reload usage examples

Related Issues

containerd/nydus-snapshotter#690

Change Details

Please describe your changes in detail:

Test Results

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Change Type

Please select the type of change your pull request relates to:

• Bug Fix
• Feature Addition
• Documentation Update
• Code Refactoring
• Performance Improvement
• Other (please describe)

Self-Checklist

Before submitting a pull request, please ensure you have completed the following:

• I have run a code style check and addressed any warnings/errors.
• I have added appropriate comments to my code (if applicable).
• I have updated the documentation (if applicable).
• I have written appropriate unit tests.

[codecov]

Codecov Report

❌ Patch coverage is 76.90418% with 94 lines in your changes missing coverage. Please review.
✅ Project coverage is 57.11%. Comparing base (8b50bbf) to head (e2bd598).
⚠️ Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
storage/src/factory.rs	13.04%	17 Missing and 3 partials ⚠️
api/src/http_endpoint_v1.rs	0.00%	19 Missing ⚠️
storage/src/backend/registry.rs	36.66%	19 Missing ⚠️
src/bin/nydusd/api_server_glue.rs	0.00%	16 Missing ⚠️
rafs/src/fs.rs	52.94%	7 Missing and 1 partial ⚠️
src/bin/nydus-image/main.rs	0.00%	3 Missing ⚠️
storage/src/device.rs	62.50%	2 Missing and 1 partial ⚠️
utils/src/config.rs	98.95%	3 Missing ⚠️
rafs/src/metadata/mod.rs	0.00%	1 Missing ⚠️
service/src/fs_cache.rs	0.00%	1 Missing ⚠️
... and 1 more

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1864      +/-   ##
==========================================
+ Coverage   56.94%   57.11%   +0.16%     
==========================================
  Files         199      200       +1     
  Lines       51623    51965     +342     
  Branches    44426    44768     +342     
==========================================
+ Hits        29398    29679     +281     
- Misses      20760    20820      +60     
- Partials     1465     1466       +1     

Files with missing lines	Coverage Δ
api/src/http.rs	0.00% <ø> (ø)
api/src/http_handler.rs	54.76% <ø> (ø)
service/src/blob_cache.rs	83.48% <100.00%> (ø)
utils/src/lib.rs	82.71% <ø> (-6.18%)	⬇️
rafs/src/metadata/mod.rs	68.15% <0.00%> (ø)
service/src/fs_cache.rs	28.39% <0.00%> (ø)
service/src/fs_service.rs	40.50% <0.00%> (ø)
src/bin/nydus-image/main.rs	0.54% <0.00%> (ø)
storage/src/device.rs	67.37% <62.50%> (+0.07%)	⬆️
utils/src/config.rs	98.95% <98.95%> (ø)
... and 5 more

... and 3 files with indirect coverage changes

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[Fricounet]

LGTM in terms of doing what we need for the mentioned issue. I'm not a big rust expert though so take my review with a pinch of salt.
Nice documentation though!

[Zephyrcf]

LGTM!

[BraveY]

LGTM