Make it possible to switch between SVG and PNG QR codes

[johannaengland]

Scope and purpose

Closes #2916. Dependent on #2897 and #2899.

Adds a config option qr_codes.file_format that gives the option to switch between generating QR codes as SVG or PNG files.

Contributor Checklist

Every pull request should have this checklist filled out, no matter how small it is.
More information about contributing to NAV can be found in the
Hacker's guide to NAV.

• Added a changelog fragment for towncrier
• Added/amended tests for new/changed code
• Added/changed documentation
  we don't currently have any documentation for QR codes - should I add some? And if so, where?
• Linted/formatted the code with black and ruff, easiest by using pre-commit
• The first line of the commit message continues the sentence "If applied, this commit will ...", starts with a capital letter, does not end with punctuation and is 50 characters or less long. See https://cbea.ms/git-commit/
• This pull request is based on the correct upstream branch: For a patch/bugfix affecting the latest stable version, it should be based on that version's branch (<major>.<minor>.x). For a new feature or other additions, it should be based on master.

[codecov]

Codecov Report

❌ Patch coverage is 86.20690% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.86%. Comparing base (9a1180a) to head (0a7cffe).
⚠️ Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
python/nav/web/utils.py	77.41%	7 Missing ⚠️
python/nav/web/__init__.py	93.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3414      +/-   ##
==========================================
+ Coverage   60.85%   60.86%   +0.01%     
==========================================
  Files         608      608              
  Lines       44198    44237      +39     
  Branches       48       48              
==========================================
+ Hits        26896    26927      +31     
- Misses      17290    17298       +8     
  Partials       12       12              

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[lunkwill42]

I don't see any reason why this should still be labeled as blocked, so I removed it.

[lunkwill42]

🎉

Approving, despite the CodeCov report, since something is up with codecov now. It should greenlight the patch coverage as long as its above the global coverage (which means >60.91% should be ok in this case)

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

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

See analysis details on SonarQube Cloud