Reasons for creating this PR

Support base href and config path variables in the environment for better docker deployment (same as SKOSMOS_SPARQL_ENDPOINT) .

Link to relevant issue(s), if any

• Closes Improved docker configuration #1865

Description of the changes in this PR

• I added env variables SKOSMOS_CONFIG_PATH and SKOSMOS_BASE_HREF.
• Updated src/model/GlobalConfig.php so when no $config_name is provided it will fallback to the env variable or the original ../../config.ttl for retro-compatibility.
• I removed the default $config_name in the constructor of src/model/Model.php which was a duplicate of GlobalConfig.php
• Allowed for $config_name and SKOSMOS_CONFIG_PATH to be either absolute (starts with /) or relative. This made me update some tests to remove the starting / in the config_name. (i.e. /../../tests/testconfig.ttl turned into ../../tests/testconfig.ttl)
• Updated tests/docker-compose.yml

Known problems or uncertainties in this PR

Some config that had defined the $config_name with a starting / might need to update the config_name.

Checklist

• phpUnit tests pass locally with my changes
• I have added tests that show that the new code works, or tests are not relevant for this PR (e.g. only HTML/CSS changes)
• The PR doesn't reduce accessibility of the front-end code (e.g. tab focus, scaling to different resolutions, use of .sr-only class, color contrast)
• The PR doesn't introduce unintended code changes (e.g. empty lines or useless reindentation)