ci: add docs check job

[oleonardolima]

Description

As we are adding in bitcoindevkit/bdk#2158, this PR adds a new CI job and justfile recipe to check for the documentation.

Notes to the reviewers

Changelog notice

### Added

- ci: add new `docs_check` job to check for any error or warning in docs.

### Changed

- fix(docs): use correct `intra_doc_links`.

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran just p before pushing

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.04%. Comparing base (4d4adae) to head (4d2e398).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #416      +/-   ##
==========================================
+ Coverage   79.93%   80.04%   +0.10%     
==========================================
  Files          24       24              
  Lines        5287     5336      +49     
  Branches      241      242       +1     
==========================================
+ Hits         4226     4271      +45     
- Misses        984      987       +3     
- Partials       77       78       +1     

Flag	Coverage Δ
rust	80.04% <ø> (+0.10%)	⬆️

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[luisschwab]

ACK 4d2e398

[Dmenec]

tACK 4d2e398

[ValuedMammal]

ACK 4d2e398

[ValuedMammal]

We should probably use --all-features here wdyt?