[MAINT] - Audit and trim REST API endpoints

[soapy1]

Context

There are some API endpoints which a clearly not used. For example, the /api/v1/specification endpoint which was broken since Oct. 2023. It would be nice to:

• understand which endpoints do not need to be supported (eg. they are unused, or no longer fit the intended usage of conda-store)
• remove unsupported api endpoints
• understand what the intended use of each REST endpoint is

Value and/or benefit

Trimming down the REST api will:

• reduce cruft to maintain
• provide users with an opinionated way to use conda-store

Anything else?

No response

[trallard]

Also relevant: our backwards compatibility policy.
If more context is needed on this @dcmcand can help fill in any gaps since he worked on such policy.