feat: Add placeholder function for future wrtc deterministic certs.

[dariusc93]

Due to libp2p-webrtc not generating deterministic certificates, this PR introduces a placeholder function that would generate such certificates in the future.

Note:

• Since rcgen uses ring rng, we may need to generate the certificate outside of rcgen so we can use rand prng, which would be seeded by us and would allow us to sign the certificate in a manner so it would be persistent.
• When libp2p-webrtc eventually supports deterministic certificate, this function may be deprecated
• One can use the utility function to generate the certificate externally and store it with the keypair to allow for it to persist across initialization, however the end-user will be responsible with the security of the certificate if that is the case.