set REG_DOMAIN and REG_SUBD automatically by the letsencrypt path

[noahehall]

export REG_CERTS_PATH=apps/nirvai-core-letsencrypt/dev-nirv-ai
export REG_DOMAIN=nirv.ai
export REG_SUBD=dev

domain & subd should default be extracted from the letsencrypt REG_CERTS_PATH
then consumers dont have to supply the domain or subdomain