Change data structure for keys so that they are not tied to the consumer entity.

This relates directly to https://www.drupal.org/project/lti_tool_provider/issues/3442192 🐛 Unnecessary client_id in the jkws url Active and offers a potential solution.

One would be able to avoid requiring the 'client_id' parameter in the jwks URL, if the system could use a a single, default keyset. Currently, that client_id is used to look up a configured consumer entity and use its keys. Since use of the client_id parameter is unusual, changing the keyset to be a site-wide configuration would remove this issue.

This would have other benefits, such as simplifying the process of key rotation for the site.

If it is somehow necessary in a certain context that some clients need their own keys, then it would be possible to retain the ability for jwks to take a client_id also. But in our experience with LTI, we find this kind of feature to not be needed.

I will fine an additional issue that also relates to this.