Support RSA signing algorithm

[btielen]

At the moment only the elliptic curve signing algorithm is supported. In the specifications it is stated that signatures can also be signed with an the RSA digital signature algorithm. Verification of such signatures would fail at the moment.

From the Health Certificate specifications

Secondary Algorithm: The secondary algorithm is RSASSA-PSS as defined in (RFC 8230) with a modulus of 2048 bits in combination with the SHA–256 hash algorithm as defined in (ISO/IEC 10118–3:2004) function 4.
This corresponds to the COSE algorithm parameter: PS256.