Create "special" index meta-database server

[CasperWA]

Since this is something all providers, who want to join the providers.json in the OPTiMaDe specification repository need to have, I suggest we create a special instance of the server that only serves the appropriate endpoints (/links and /info), with a JSON file that can be altered for each implementation provider.

Essentially, it will utilize the enhancements introduced by PRs #95 and #99 to serve specific endpoints and load a JSON file similarly to how we currently load test entries.

This server may be started with a separate bash script or by editing the script so that one can pass a desire to switch to a different FastAPI application.

[CasperWA]

A beginning of this (using the commits also from #95 and #99) has been created under the branch index_meta_db.