docs: Specified that the API template only supports images for now

[fg-mindee]

Following up on some QA feedback, this PR introduces the following modifications:

• specifies that all routes support only images and not PDF for now
• cleaned the expected route status
• improved the CI check: it used to check that the base URL is accessible, and now it will check whether it can access the swagger/docs

Any feedback is welcome!

cc @RBMindee

[codecov]

Codecov Report

Merging #609 (9151f63) into main (250a3cb) will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #609      +/-   ##
==========================================
- Coverage   96.06%   96.03%   -0.03%     
==========================================
  Files         110      110              
  Lines        4265     4265              
==========================================
- Hits         4097     4096       -1     
- Misses        168      169       +1     

Flag	Coverage Δ
unittests	96.03% <ø> (-0.03%)	⬇️

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

Impacted Files	Coverage Δ
...dels/detection/differentiable_binarization/base.py	91.19% <0.00%> (-0.63%)	⬇️

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[charlesmindee]

Thanks for the PR!