Added available() method and check_url to argument to Triplestore

[jesper-friis]

Description

Integrated checking if a backend service is available to the standard Triplestore API, by adding the available() method and check_url to argument to the Triplestore class.

The check_url configuration can now be configured together with other parameters in the session.

Simplified tests by using sessions and the new check_url configuration.

Type of change

• Bug fix and code cleanup
• New feature
• Documentation update
• Testing

Checklist for the reviewer

This checklist should be used as a help for the reviewer.

• Is the change limited to one issue?
• Does this PR close the issue?
• Is the code easy to read and understand?
• Do all new feature have an accompanying new test?
• Has the documentation been updated as necessary?
• Is the code properly tested?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.88%. Comparing base (7996b53) to head (29d5fa9).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #437      +/-   ##
==========================================
+ Coverage   83.86%   83.88%   +0.01%     
==========================================
  Files          29       29              
  Lines        4109     4114       +5     
==========================================
+ Hits         3446     3451       +5     
  Misses        663      663              

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[francescalb]

What does this mean?

[jesper-friis]

I have now updated the docstring to the following:

    interval: Internal time interval in seconds between checking if the
        service has responded.

Is that more understandable?