Documentation of test interface for the implementer, in addition to the spec

[lukehesluke]

Provide very clear guidance on what each Action specifically needs to do, and which need to be implemented depending on the features implemented

Ensure that this guidance is signpostable from the following places:

• The auto-generated documentation from Test Suite, which indicates which actions need to be implemented (https://github.com/openactive/openactive-test-suite/issues/654) e.g. in the "Test prerequisites"-headed section
• The Test Interface spec
• The OBA implementation guide (maybe in key decisions?)

Specifically consider how test data generation can be used to narrow down which criteria need to be implemented, which reduces work for the implementer

Potentially improve the test data generation tool with a flag to produce this data more clearly LW: That task has separately been defined here: https://github.com/orgs/openactive/projects/17/views/1?pane=issue&itemId=38590522. Probably, that task should be completed first, so that the documentation consists of instructing users to use that new logic

[lukehesluke]

Gitbook PR: https://app.gitbook.com/o/-LJTExWaXZFqcFJ_lZwF/s/-LOMz1IIOd5fl4xzfUYb/~/diff/~/changes/275/open-booking-api/key-decisions (now merged)