Should `v1/agent/connect/ca/roots` respond with a 200 status code with 0 roots in the response

Prior to this #7142 we were making the assumption that a 200 status code from the endpoint would indicate that bootstrapping was finished. However in reality the 200 was not indicating that any roots had been created nor the active root assigned.

#7142 unflaked the test that we saw failing periodically but left me with the open question of whether returning 200 in this case is desirable?

Start with the v1/agent/connect/ca/roots endpoint and the test discussed in #7142. Review how a 200 response is interpreted when zero roots exist and determine the intended status-code contract. Done means the expected behavior is decided and reflected in the relevant test or documentation.

Written by the indexing model from the issue text.