feat: Buckets & MOS plugins in ExternalFrames in Dashboard

[jstarpl]

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

Adds the Bucket concept and enables ExternalFrame guests to use MOS HTML5 Plugin API

• What is the current behavior? (You can also link to an open issue here)

• What is the new behavior (if this is a feature change)?

• Other information:

Status

• The functionality has been tested by the PR author
• The functionality has been tested by NRK

[jstarpl]

Looks good from initial glance (I've only looked at the server-side parts).

It needs to be rebased onto release20 and functionality-tested again before merging, I think.

Rebased onto release20 and should be ready for feature-testing along with Ola's updated MOS plugin.

[codecov-io]

Codecov Report

Merging #195 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #195   +/-   ##
=======================================
  Coverage   66.96%   66.96%           
=======================================
  Files         151      151           
  Lines        9958     9958           
  Branches     2230     2230           
=======================================
  Hits         6668     6668           
  Misses       3256     3256           
  Partials       34       34           

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[jstarpl]

I just realized we should wait for testing before we merge, so that we don't cause any more mess in the workflow. This should now be ready for merging.