Add RSA key

[clehner]

Add RSA key with 2048-bit modulus.

This key was generated using the jose CLI tool (jose jwk gen -i '{"kty":"RSA","bits":2048}')

Reference for key representation: https://datatracker.ietf.org/doc/html/rfc7518#section-6.3

Implementations should use the PS256 JWS algorithm, as specified in lds-jws2020:

• https://github.com/w3c-ccg/lds-jws2020/#supported-jose-algorithms
• https://w3c-ccg.github.io/lds-jws2020/#jose-conformance