Support a CSV list for `HMA_WORKER_ROLE`

[turt2live]

see title :)

[theoteske]

Hello, I'm new to this repo and I'm interested in contributing. Is this issue still relevant, and if so, are there any guidelines I should keep in mind for a PR?

[turt2live]

Hello! The issue is very much still relevant. Contributing guidelines are available at https://github.com/matrix-org/hma-matrix?tab=contributing-ov-file and the code should be pretty straightforward, hopefully.