plutus-pab: swagger docs - endpoint schema specs

[OlofBlomqvist]

Describe the feature you'd like

I think endpoints such as the 'endpoint endpoint' below should be separated in to whatever endpoints actually exists rather than having them be a path variable, and made so that the applicable schema information for each one is available.

Right now, the documentation just says I should send a "string", which is really no help at all.. not for me, and not for a generated client.

Describe alternatives you've considered

One could probably also use "oneOf" to describe the different allowed inputs to the same endpoint (see https://swagger.io/docs/specification/describing-request-body/)..