feat: add canonical URL slug on files

[fabien-michel]

Description

Add a canonical URL slug as an alternative to numbered canonical URL

Related resources

• https://discourse.django-cms.org/t/add-a-canonical-slug-to-django-filers-files/237/2

Checklist

• [x] I have opened this pull request against master
• [x] I have added or modified the tests when changing logic
• [x] I have followed the conventional commits guidelines to add meaningful information into the changelog
• [x] I have read the contribution guidelines and I have joined #workgroup-pr-review on Slack to find a “pr review buddy” who is going to review my pull request.

[codecov[bot]]

Codecov Report

Merging #1300 (7503ea5) into master (dc6afa0) will decrease coverage by 0.24%. The diff coverage is 86.84%.

@@            Coverage Diff             @@
##           master    #1300      +/-   ##
==========================================
- Coverage   72.21%   71.96%   -0.25%     
==========================================
  Files          72       67       -5     
  Lines        3239     3157      -82     
  Branches      563      551      -12     
==========================================
- Hits         2339     2272      -67     
+ Misses        734      730       -4     
+ Partials      166      155      -11     

Impacted Files	Coverage Δ
filer/admin/fileadmin.py	88.23% <75.00%> (+0.73%)	:arrow_up:
filer/models/filemodels.py	86.63% <88.00%> (+0.09%)	:arrow_up:
filer/migrations/0016_file_canonical_url_slug.py	100.00% <100.00%> (ø)
filer/urls.py
filer/views.py
filer/migrations/0001_initial.py
filer/apps.py
filer/__init__.py
filer/settings.py

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[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale[bot]]

This will now be closed due to inactivity, but feel free to reopen it.