Use session-based Spoke Portal magic link

[bchrobot]

Is your feature request related to a problem? Please describe.

https://github.com/politics-rewired/spoke-portal/pull/165 adds support for authenticated magic link sessions. This changes requires a JWT query parameter in the link provided to Spoke users.

Describe the solution you'd like

Spoke needs to update the tcrBrandRegistrationUrl field to include this JWT:

Spoke/src/server/lib/notices/register-10dlc-brand.ts

Lines 106 to 113 in e3b9e78

	return [
	{
	__typename: "Register10DlcBrandNotice",
	id: messagingServiceSid,
	tcrBrandRegistrationUrl: `https://portal.spokerewired.com/10dlc-registration/${messagingServiceSid}`
	}
	];
	}

This will required:

1. Adding an envvar for the signing secret shared between Spoke and Spoke Portal
2. Adding a root resolver for Notices to support fetching a tcrBrandRegistrationUrl at runtime when an admin user clicks the Notice call-to-action. This is because the generated JWTs should have an expiration of only ~30 seconds for security.

Describe alternatives you've considered

N/A

Additional context

N/A