Ensure that space application supporter can get/list buildpacks

[philippthun]

• Add tests that check permissions.

Closes #2217.

• I have reviewed the contributing guide

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

• 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

[sweinstein22]

Acceptance

Confirmed user only has space_application_supporter and organization_user roles:

$ cf curl /v3/roles?user_guids="0776980f-9ea5-499a-9a23-ecc09d0d5b39"
{
  ...
  "resources": [
    {
      "guid": "7555955f-5baf-4700-93e1-3952ef664a1f",
      "type": "organization_user",
      "relationships": {
        "user": {
          "data": {
            "guid": "0776980f-9ea5-499a-9a23-ecc09d0d5b39"
          }
        },
      ...
    },
    {
      "guid": "e158488c-2b95-4806-a6f1-68df9dde8fdc",
      "type": "space_application_supporter",
      "relationships": {
        "user": {
          "data": {
            "guid": "0776980f-9ea5-499a-9a23-ecc09d0d5b39"
          }
        },
       ...
  ]
}

Ran cf curl against /v3/buildpacks and /v3/buildpacks/:guid as both a space developer and a space application supporter. Confirmed that there was no diff, and manually confirmed that output looked correct:

$ diff /tmp/space-dev-buildpacks /tmp/space-app-supporter-buildpacks

$ diff /tmp/space-dev-buildpack-guid /tmp/space-app-supporter-buildpack-guid

Code Review

Changes looks good, converts to using the shared example structure for permissions tests. As the endpoint was already available to all roles only testing changes were required.

Docs

No changes required, as the docs already indicate that these two endpoints are available to all roles.

Looks good, thanks for the PR!