Add /v3/service_instance/:guid/permissions endpoint

[FloThinksPi]

• A short explanation of the proposed change:

Add the /v3/service_instance/:guid/permissions endpoint that enables service_instance dashboard functionality with the V3 API

• An explanation of the use cases your change solves

As a service developer there is a functionality called service dashboards (https://docs.cloudfoundry.org/services/dashboard-sso.html#checking-user-permissions). These dashboards call the CF API to check if a user is allowed to alter or read the service_instance. This is done via /v2/service_instance/:guid/permissions. A corresponding V3 endpoint does not exist which means this functionality wont work anymore when V2 is disabled.

This PR adds this endpoint also in V3.

See also https://cloudfoundry.slack.com/archives/C07C04W4Q/p1657878898740599

• [x] I have reviewed the contributing guide

• [x] I have viewed, signed, and submitted the Contributor License Agreement

• [x] I have made this pull request to the main branch

• [ ] I have run all the unit tests using bundle exec rake

• [ ] I have run CF Acceptance Tests