Add build matrix with CentOS to GH Actions

[robertopreste]

Closes #557

This PR adds a second workflow that targets CentOS 7, only installing Symphony Remote on this platform. Tests are run separately in the Ubuntu workflow.

[codecov-commenter]

Codecov Report

Merging #558 (ca2f30b) into master (4b07ecd) will not change coverage.
The diff coverage is n/a.

❗ Current head ca2f30b differs from pull request most recent head 6169a52. Consider uploading reports for the commit 6169a52 to get more accurate results

@@           Coverage Diff           @@
##           master     #558   +/-   ##
=======================================
  Coverage   95.10%   95.10%           
=======================================
  Files          92       92           
  Lines        4168     4168           
  Branches      269      269           
=======================================
  Hits         3964     3964           
  Misses        144      144           
  Partials       60       60           

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[flongford]

Thanks @robertopreste! I only have a few minor comments, can re-review whenever

[flongford]

LGTM!