refactor: redirect to original image if thumbnail is inaccessible

[guqing]

What type of PR is this?

/kind improvement
/area core
/milestone 2.19.x

What this PR does / why we need it:

获取缩略图时检查缩略图链接是否可访问否则重定向到原图链接

Does this PR introduce a user-facing change?

获取缩略图时检查缩略图链接是否可访问否则重定向到原图链接

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 4 lines in your changes missing coverage. Please review.

Project coverage is 57.98%. Comparing base (6cd8dc8) to head (5dd91e6).
Report is 43 commits behind head on main.

Files with missing lines	Patch %	Lines
...ore/attachment/impl/LocalThumbnailServiceImpl.java	0.00%	2 Missing ⚠️
...run/halo/app/theme/endpoint/ThumbnailEndpoint.java	85.71%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6556      +/-   ##
============================================
- Coverage     58.18%   57.98%   -0.20%     
- Complexity     3774     3883     +109     
============================================
  Files           651      670      +19     
  Lines         22125    22880     +755     
  Branches       1538     1551      +13     
============================================
+ Hits          12873    13267     +394     
- Misses         8641     9002     +361     
  Partials        611      611              

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[ruibaby]

/lgtm

[JohnNiang]

/approve

[f2c-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: JohnNiang

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