Added test for installing from distribution packages

[hummeltech]

In order to ensure that the instructions contained within README.rst also work when installing mod_tile packages from Debian/Ubuntu repositories, I have added a basic test which first installs those packages and then executes the same commands from the aforementioned instructions.

Here is an example of a workflow run:
https://github.com/hummeltech/mod_tile/actions/runs/5638547864

Also:

• Add additional image format types into example configuration instructions in README.rst
  • Which are already referenced in utils/example-map/index.html
• Add step in README.rst to ensure /var/run/renderd exists

[codecov-commenter]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (184f143) 44.96% compared to head (d5dcb4c) 44.92%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #330      +/-   ##
==========================================
- Coverage   44.96%   44.92%   -0.05%     
==========================================
  Files          23       23              
  Lines        4577     4577              
==========================================
- Hits         2058     2056       -2     
- Misses       2519     2521       +2     

see 1 file with indirect coverage changes

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