Consider implementing "semver" checks for REST APIs

[m4tx]

When we have automatic OpenAPI spec generation for the REST API endpoints, we might consider doing "semver" checks that would perform a diff between versions of the OpenAPI specs and return whether incompatible changes in the APIs were made (either in the input or the output of an endpoint).

This would allow us to do (semi-)automatic API versioning. The open question is how useful that would be and where to implement it (probably not directly in the cot crate itself, but perhaps in the CLI?)