support configuration change using API calls

[andaaron]

Currently the zot sync configuration can be changes only by modifying the zot configuration file.
We should implement an API to update this sync configuration, so other service can modify it while zot is running.

At a minimum we should be able to specify what images and tags we need to sync for a given registry.

[rchincha]

Originally for some specific parts of the configuration, but should really be generally be applicable.

This can be a mgmt "extension".

POST, PUT /v2/_zot/mgmt/<>

[rchincha]

IMO, this feature should be designed as a "config" extension [1]

When a user wants to know if this is a zot that can dynamically update mgmt via APIs, then
GET /v2/_oci/ext/discover should return /v2/_zot/ext/config in the supported extensions list.

A user can assume /v2/_zot/ext/config and interact with it directly.

A user can
GET /v2/_zot/ext/config/ to get the current configuration
POST /v2/_zot/ext/config/ to do a full POST of configuration
PATCH /v2/_zot/ext/config/ to patch specific sections of configuration

Before applying any config changes:
Validate config
Evaluate impact
Permissions, authN, authZ

References:
[1] https://github.com/opencontainers/distribution-spec/tree/main/extensions