CI: add Dependabot

[pjonsson]

Make Dependabot update the actions
and Dockerfile.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.47%. Comparing base (ec63f09) to head (8a8f0aa).
Report is 59 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #634      +/-   ##
===========================================
- Coverage    76.71%   76.47%   -0.24%     
===========================================
  Files           41       41              
  Lines         2998     3061      +63     
===========================================
+ Hits          2300     2341      +41     
- Misses         698      720      +22     

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[omad]

Thanks