feat(registration): add member repository

[dasher1505]

No description provided.

[WilliamTayNZ]

good work! just a few things

[WilliamTayNZ]

Good work Dasher 🔥 almost ready to go, just a few tiny changes, see comments

Also, since createMembershipRegistration is an important function which actually creates the membership registration, it would be good to specify an explicit contract for what it returns:

type CreateMembershipRegistrationResult =
  | { ok: true }
  | { ok: false; error: { type: "duplicate" | "database" } };

The function's return type should wrap the result type in a Promise, since the function is asynchronous.

Well done

[WilliamTayNZ]

good work!