feat(api): add signup.handler option and check signup.enabled

[xmaxcooking]

• Splits the signup and login validation and checks the dbAuthHandler signup.enabled now.
• Adds a signup.handler for any actions after a user gets created.

can be used like this:

  const oAuthHandler = new OAuthHandler(event, context, authHandler, {
    // The name of the property you'd call on `db` to access your OAuth table.
    // i.e. if your Prisma model is named `OAuth` this value would be `oAuth`, as in `db.oAuth`
    oAuthModelAccessor: 'oAuth',
    // You can instead do `enabledProviders: {}`, but I find it more clear to be explicitly not enabling these
    // We'll enable at least one of these later on, but leave it like this for now
    enabledProviders: { apple: false, github: false, google: true },

    signup: {
      // The signup handler is called after a user has been successfully created
      handler: async (user) => {
        await sendConfirmationEmail(user.id)
        return user
      },
    },
  })

[arimendelow]

This is awesome!! Thanks @xmaxcooking :)