Clean up circular generation

Currently circulars get a lot of their information from the voevent, and it looks like ligo-followup-advocate will need to get even more information from the voevent in order to fix #664 (closed). We should change this before O4b such that we can pass in the relevant filenames to the circular generation function call. The following is a short list of changes that would need to be made, but there are probably other changes not represented here.

• Modify function in ligo-followup-advocate to take filenames
• Modify the "generate update circular" button in our dashboard to take filenames like the "send update notice" feature
• Modify the orchestrator to send the filenames to the circular generation function