Store attorneys for an oral argument

[grossir]

On some oral argument sources, we can collect the "attorneys" field. Most recently seen in cadc by @flooie

There is a Docket.parties field, but those are objects, not strings.

We should have in the Audio model an attorneys field, similar to the one existing on OpinionCluster:

courtlistener/cl/search/models.py

Lines 2591 to 2594 in ec8bc90

	attorneys = models.TextField(
	help_text="The attorneys that argued the case, as free text",
	blank=True,
	)

Another proposed modification to the Audio model: #4195

[v-anne]

5th Circuit does too, but formatting isn't that great:
https://www.ca5.uscourts.gov/oral-argument-information/oral-argument-recordings