chore: skip orchestrator info requests if service uri not set by orchestrator

[ad-astra-video]

What does this pull request do? Explain your changes. (required) Update db_discovery.go to skip starting orchestrator http client if the service uri is not set by the orchestrator. At time of this commit, 71 orchestrators have not registered for the AI subnet so this skips a lot of failed http connections.

Docker build is at docker pull adastravideo/go-livepeer:ai-video-test

Specific updates (required)

• add a check to confirm a Host exists in the parsed service uri.

How did you test each of these updates (required) Built docker file and started up gateway startup.log

Checklist:

• [ ] Read the contribution guide
• [X] make runs successfully
• [ ] All tests in ./test.sh pass
• [ ] README and other documentation updated
• [ ] Pending changelog updated