Skosmos 3 docker: upgrade to Ubuntu 22.04 base image and PHP 8.1

[osma]

Reasons for creating this PR

Skosmos 3 needs a recent PHP version (currently 8.0 or 8.1) but the Dockerfile we are using for running Skosmos is based on Ubuntu 20.04 which has PHP 7.4. This PR upgrades to a more recent Ubuntu 22.04 base image which has PHP 8.1.

Link to relevant issue(s), if any

• prerequisite for properly running Cypress tests using dockerized Skosmos, e.g. Run cypress #1479

Description of the changes in this PR

• upgrade to Ubuntu 22.04 base image
• adjust system and PHP packages (gettext shouldn't be needed anymore)

Known problems or uncertainties in this PR

Not 100% sure if this is the right set of packages and PHP extensions, but we can fix that later if there are any problems.

Checklist

• phpUnit tests pass locally with my changes
• I have added tests that show that the new code works, or tests are not relevant for this PR (e.g. only HTML/CSS changes)
• The PR doesn't reduce accessibility of the front-end code (e.g. tab focus, scaling to different resolutions, use of .sr-only class, color contrast)
• The PR doesn't introduce unintended code changes (e.g. empty lines or useless reindentation)

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (cdcc15b) 63.89% compared to head (4eb7107) 63.89%.

Additional details and impacted files

@@             Coverage Diff              @@
##             skosmos-3    #1498   +/-   ##
============================================
  Coverage        63.89%   63.89%           
  Complexity        1634     1634           
============================================
  Files               32       32           
  Lines             4290     4290           
============================================
  Hits              2741     2741           
  Misses            1549     1549           

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