add indexes for transcription model to aid with transcribot queue

[itsthejoker]

Relevant issue: https://github.com/GrafeasGroup/blossom/pull/163

Description:

Just adds a few indexes on the Transcription model to try and get times down.

Checklist:

• [x] Code Quality
• [x] Pep-8
• [ ] Tests (if applicable)
• [x] Success Criteria Met
• [ ] Inline Documentation
• [ ] Wiki Documentation (if applicable)