test API

[fmeynadier]

I finally tried to brush up the "test API" section (uvicorn/fastAPI).

Many links are broken but I think it is because of unsynchronised updates somewhere else, not necessarily because I moved the files and changed some hard coded paths (but some things are broken because of this, too...).

I began to perform changes on "fix_test_api" branch, melting it with the recent changes and transition to a package.

In this branch you can simply start it with command "launch_si_api" (see '-h' for available options).

I am not sure how important it would be to reach full functionality here, given that this is not the final API. I see that as a test sandbox for queries and interface, right ?