Add support for signing with a RSA PEM private key: `pkcs8` and `pkcs1`.
Fixes https://github.com/denoland/deno/issues/18972
Ref #21124
Verified fix with `npm:sshpk`. Unverfied but fixes
`npm:google-auth-library`, `npm:web-push` & `oracle/oci-typescript-sdk`
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Signed-off-by: Divy Srivastava <dj.srivastava23@gmail.com>
