MINOR: jwt: Add support for RSA-PSS signatures (PS256 algorithm)

MINOR: jwt: Add support for RSA-PSS signatures (PS256 algorithm)

This patch adds the support for the PS algorithms when verifying JWT
signatures (rsa-pss). It was not managed during the first implementation
and previously raised an "Unmanaged algorithm" error.
The tests use the same rsa signature as the plain rsa tests (RS256 ...)
and the implementation simply adds a call to
EVP_PKEY_CTX_set_rsa_padding in the function that manages rsa and ecdsa
signatures.
The signatures in the reg-test were built thanks to the PyJWT python
library once again.