Remove garvan url from prisma schema `tcLink` default

[ignatiusm]

Currently Ln124 of application/backend/prisma/schema.prisma sets default Terms and Conditions link (tcLink) to be a Garvan site:

  tcLink          String  @default("https://garvan-data-science-platform.github.io/ctrl-docs/docs/terms-and-conditions")

If other organisations are going to deploy CTRL they are not going to want to point to Garvan terms and conditions. I suggest this should be blank by default.

Also, by not having a default, this can force the deploying Organisation to actively populate the tcLink when deploying the Application.

[ignatiusm]

application/backend/srec/controllers/AuthController.test.ts has a test that checks the /auth/tcs endpoint - this test may need to be updated (or use a seeded value).

and also application/backend/src/controllers/SettingsController.test.ts