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
- ci(msrv): pin `icu_*` dependencies for 1.85.0 supported MSRV
- 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 (826b19f) to head (8b4a51e).
⚠️ Report is 4 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #416   +/-   ##
=======================================
  Coverage   80.04%   80.04%           
=======================================
  Files          24       24           
  Lines        5336     5336           
  Branches      242      242           
=======================================
  Hits         4271     4271           
  Misses        987      987           
  Partials       78       78           

Flag	Coverage Δ
rust	80.04% <ø> (ø)

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[luisschwab]

ACK 4d2e398

[Dmenec]

tACK 4d2e398

[ValuedMammal]

ACK 4d2e398

[oleonardolima]

I pushed 2f2346e to fix MSRV CI.

[luisschwab]

ACK 8b4a51e

[ValuedMammal]

Thank you!

[ValuedMammal]

ACK 8b4a51e