Fix system prompt of analyze link

[gduquesnay]

Our 'analyze” link had a hard-coded system prompt “You are a helpful assistant” the prompt in the config.yml is being sent as the “user” message along with the transcript appended:

{"role": "user", "content": prompt + "\\n\\n" + transcript}, 

When the transcript is too short this creates a confusing prompt since it isn’t obvious that it IS the transcript rather than part of the instructions.

• Allow for the system prompt to be customized while keeping the current "You are a helpful assistant" as the default.
• Add a default empty string value for the "prompt"
• Add unit tests for the analyze link

[linear]

VCO-35