Allow loading selected projects using environment variable

[juhoinkinen]

This PR makes it possible to select the projects that Annif loads on startup via a regexp pattern given in the environment variable ANNIF_PROJECTS_INIT. The same env can be used in NGINX in its location directive configuration to make NGINX pass a request to the Annif instance that has loaded the requested project.

An image with these changes has been running at ai.dev.finto.fi. The used helm-chart includes grouping projects with these environment variables:

yso-.*fi
yso-.*sv
yso-.*en
kauno-.*
thema-.*
ykl-.*

Closes #733.

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.65%. Comparing base (eba2b0c) to head (54ee767).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #774   +/-   ##
=======================================
  Coverage   99.65%   99.65%           
=======================================
  Files          89       89           
  Lines        6404     6422   +18     
=======================================
+ Hits         6382     6400   +18     
  Misses         22       22           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.