(OPTIONALLY) Validate that accessService.endpointUrl does not end in a trailing `/` (for Dataset Site)

[lukehesluke]

Test Suite currently tests this (see: packages/openactive-integration-tests/test/features/core/dataset-site/implemented/dataset-site-jsonld-valid-test.js).

If this is a constraint that we agree upon, then it should be imposed at Validator rather than at Test Suite.

However, I'm not fully convinced that this is necessary. The comment for that test in Test Suite says:

(as per Open API 3 Base URL https://swagger.io/docs/specification/api-host-and-base-path/)

However, I don't see how that doc enforces that paths cannot end in a trailing / — and that doc is about Open API, which is unrelated to Dataset Site.

So the task is to:

• decide on whether to enforce this or not
• If enforcing, move the validation to Validator (and document it in the spec!)
• If not enforcing, remove the check from Test Suite

Pros of enforcing:

• Consistency may reduce the chance of user error

Cons of enforcing:

• Reduces configuration flexibility