Add support for OKP key type validation

[orelmaliach]

As per

strimzi-kafka-oauth/oauth-common/src/main/java/io/strimzi/kafka/oauth/validator/JWTSignatureValidator.java

Lines 396 to 403 in 399a19f

	if (jwk instanceof ECKey) {
	publicKey = ((ECKey) jwk).toPublicKey();
	} else if (jwk instanceof RSAKey) {
	publicKey = ((RSAKey) jwk).toPublicKey();
	} else {
	log.warn("Unsupported JWK key type: {}", jwk.getKeyType());
	continue;
	}

when an auth server returns JWK key whose type is OKP, it's not being added to validator cache, and later kafka fails to authenticate with error:
Failed authentication - Token validation failed: Unknown signing key. Only RSA/EC key types are supported.

Would it be possible to add support for validating JWTs with OKP key type?