[to be closed] api: Add OpenAPI schema & swagger-ui

[R2ZER0]

This PR has grown more than I'd like it to, it:

• adds support for OpenAPI 3.0 schema w/ swagger-ui via drf-spectacular
• Incorporates the 360G schema w/ conversion from JSONSchema to OpenAPI 3.0
• Moves the public API out of experimental into it's own module
• Scales-back what it displays compared to the current live, so we

[R2ZER0]

This PR has been split into three parts, #178, #179 and #181 so closing.