[_] feat: add hybrid encryption support for pre created users

[apsantiso]

We need to add support for pre-created users' Kyber keys. This PR enables the backend to generate temporary Kyber keys while also allowing hybrid-encrypted invitations to be updated with frontend-generated keys when the user registers.

Changes

• Added support for pre-created users' Kyber keys.
• The backend now generates temporary Kyber keys for pre-created users.
• Hybrid-encrypted invitations are updated with frontend-generated keys when the user registers.
• Hybrid-encrypted invitations that belongs to pre-created users without any kyber key and/or new kyber keys are not re generated when users register, get deleted. This is an edge case but it is possible if user registers from any source that does not provide kyber keys.
• Added an import helper for ESM packages. Since NestJS compiles into CommonJS and is written in TypeScript, we cannot import ESM libraries traditionally. NestJS does not support ESM yet, and a standard dynamic import won't work due to TypeScript compilation. See this example in NestJS's official repo.
• Added Kyber KEM as a provider, initializing it on bootstrap to avoid using dynamic imports on every request.

Updated Endpoints

• POST /users/: Now updates hybrid-encrypted invitations when a pre-created user registers.
• POST /users/pre-created/register: Now updates hybrid-encrypted invitations when a pre-created user registers.
• POST /users/pre-created/: Now generates Kyber keys alongside ECC keys.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
86.9% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[sg-gs]

I find the cryptography tests a bit weak. The main reason is that we are mocking the underlying libraries doing the hard thing, which is not the best way to ensure this does not get broken.

It would be better to use NIST cases hardcoded here so we assert the same things that some of the best cryptography experts in the world consider valid to ensure the validity of algorithms like Kyber.

Therefore, I invite @TamaraFinogina here to join the review as she has done that on drive-web