feat: add support for avif contact avatars

[st3iny]

Requires nextcloud/server#49981 or nextcloud/server#51195

Ref https://www.garykessler.net/library/file_sigs.html (for a list of magic file headers)

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 11.13%. Comparing base (44f4c7b) to head (62f3060).
Report is 17 commits behind head on main.

Files with missing lines	Patch %	Lines
...components/ContactDetails/ContactDetailsAvatar.vue	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #4369      +/-   ##
============================================
- Coverage     11.13%   11.13%   -0.01%     
  Complexity      265      265              
============================================
  Files           122      122              
  Lines          5541     5543       +2     
  Branches       1185     1186       +1     
============================================
  Hits            617      617              
- Misses         4802     4805       +3     
+ Partials        122      121       -1     

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