createWithMtlsJavaKeystore should use custom key operations to support non-exportable keys

Feature Request:

https://github.com/awslabs/aws-crt-java/blob/54af47133f21e6bfe8eb1dc1aea9adced4911e3c/src/main/java/software/amazon/awssdk/crt/io/TlsContextOptions.java#L373

createWithMtlsJavaKeystore extracts the key, assumes it is RSA and then creates the TLS options using the in-memory private key and certificate. There should be a way to use the Java KeyStore via custom key operations to provide security without exporting the key from secure storage such as PKCS11 or AndroidKeyStore.

This can be done by customers manually by writing the necessary code, but having a prebuilt implementation to call the necessary Java APIs to sign and verify using the secure key material would make a lot of sense.