fix: Allow screen IDs to have any format

[jzimbel-mbta]

Asana task: Permanent Config GL E-Ink QA (Too-strict screen ID validations)

The validation code enforced a particular format on the GL e-ink screen IDs, but we don't need that.

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Notes for posterity:

• The other validation issue found during eng QA, where duplicate screen IDs were not always caught, was actually just one more symptom of the auth issue that Christian fixed in fix: User Session TTL #277.
• I originally went down a rabbit hole trying to fix a large number of issues with state value mutation on the client, but ended up dropping that work in favor of a more surgical fix. In case we do end up finding problems caused by the mutations in the future, I've pushed my WIP, semi-broken code to the jz/fix-pending-screen-validation as a possible reference or starting point for a more complete fix.

[cmaddox5]

May be a design/product question, but if we aren't doing these checks anymore should we bother pre-populating the field? When a new row is added, it will have EIG- in the box. Is that necessary?

[jzimbel-mbta]

@cmaddox5 I think it's good as-is. That's a convenience thing since in most cases the IDs will follow that format. We just don't want to stop people from using a different format if they feel the need.