Add round_id regex validation pattern

[annakrystalli]

In the round_id property, if round_id_from_variable: false add a regex pattern to ensure the round IDs conform to expected pattern of either:

1. an ISO date
2. any combination of letters, numbers or hyphen (_)

The following pattern should do: ^(\\d{4}-\\d{2}-\\d{2})|[A-Za-z0-9_]+$ but also consider: hubverse-org/hubValidations#135