test for titiler-pgstac api

[emileten]

This PR adds :

• a test of the mosaic/register titiler pgstac endpoint
• a test of the mosaic/{searchid}/tiles/z/x/y/assets endpoint
• simplifies the environment, by inferring the URLs from the domain names we recently added to the environment (rather than having separate variables for it)
• removes some unused files.

It's a "silly" test that use the single test collection and item we have : I register a mosaic through mosaic/register with an item search that has no filter, simply the name of our test collection (test_collection). So the mosaic is going to be composed of all the items we have in the collection after the ingestion tests ran (namely, just one). Once the mosaic is registered, I test that I can find through the mosaic/{searchid}/tiles/z/x/y/assets endpoint, a single item with the expected assets (tif and csv, based on our test data).

The goal is just to verify that the basic functionality works.

[emileten]

@jjfrench @omshinde alright the test tests action passed. Shall we run these in dev as well? Also can someone review when you get a chance ? Thank you !