MA3 Provider Onboarding - Sign Up

[davidtaing]

• add new Sign Up page for Service Providers at /service-providers/sign-up.
• change how roles are saved in metadata when creating new users.
• update users table and trigger to handle role metadata.

TODO in follow up PRs:

• need to plan out the onboarding flow for Stripe Accounts.
  • create onboarding link
  • track Stripe onboarding completion (webhook handler?)
  • plan out how the Service Provider user will create their public profile.