Right now we support RS256, RS384 and RS512 JWT signing algorithms. This ticket will add support for PS256.

PS256 is similar to RS256 but uses a different padding scheme (PSS - Probabilistic Signature Scheme) instead of PKCS#1 v1.5 padding. This requires different OpenSSL functions to verify and validate tokens signed with it.

Work required:
In `jws_validator_openssl.cpp`:

1. Add new kPS256 constant and update getHashingAlg() method.
2. Add new validation path for PSS algorithms using EVP_PKEY_CTX instead of EVP_MD_CTX.
3. Take into consideration extra algorithms could be added in the future.

In `jws_validated_token_test.cpp`:

1. Add unit tests for PS256 JWT.