[Feature] LinkML Schema Service: API Interface

[infispiel]

The purpose of this issue is to create the server stub that handles receiving and responding to API calls to handle schema server functionality.

Currently, the service is planned to:

• Create a /v1/ui html endpoint for interactive use of the API.
• Support 'default' operations on the /schemas/ endpoint
  • GET (receive a paginated list of all schemas in the DB)
    • BUGFIX: Response does not currently align to API schema.
      • Response is correct, OpenAPI Schema has bad examples.
  • PUT (put a new schema)
• Support 'id' operations on the /schemas/{id} endpoint
  • GET
  • DELETE
  • PATCH
  • PUT
• Support Schema validation on the /schemas/validate endpoint
  • Moved to [Feature] LinkML Schema Service: Validate a LinkML Schema for processability #1882
  • Endpoint itself exists
• Support Metadata validation on the /schemas/{id}/validate endpoint
  • Moved to [Feature] LinkML Schema Service: Validate LinkML Metadata against a Stored Schema #1883
  • Endpoint itself exists

Importantly, this service is not the de facto ground truth for the schema of the API. Therefore, it comes with a script to adjust the current ground truth schema into a format it can hand to Connexion to automatically set up certain functionality.
(Currently, this script treats the OpenAPI schema like plaintext -- for stability reasons, it should eventually be updated to actually parse it like the yaml it is.)

• Script to turn OpenAPI schema into schema sufficient for Connexion
• Update script to be more stable (treat schema like YAML)
  • Moved to [Refactor] LinkML Schema Service: Update OpenAPI Adjustment Script to treat schema like YAML #1884

[infispiel]

Will peel remaining TODOs into their own issues as they're not necessary to say this component is ready for review.