Test Suite users should use openactive-openid-test-cli to verify OIDC auth before running tests

[lukehesluke]

Signpost to Test Suite users that they should use openactive-openid-test-cli on their OpenID Connect auth implementations (if they have implemented OIDC as described here in the spec: https://openactive.io/open-booking-api/EditorsDraft/#openid-connect-booking-partner-authentication-for-multiple-seller-systems).

If they run the tests without verifying their OIDC implementation, they may get a barrage of errors, as almost nothing will work. This might overwhelm then and so it would be better for them to use the CLI first.

Find instructions on how to run the CLI in packages/openactive-openid-test-cli/README.md in the Test Suite project.

As a guideline, it seems that this information should be easily accessibly by a developer who is reading through the Testing Booking section in the dev docs. Particularly where OIDC is discussed

Spawned from openactive/openactive-test-suite#633