Feature: mTLS support for the psp_executor HTTP API into op-defender

[Ethnical]

Is your feature request related to a problem? Please describe.
This feature would increase the security of the HTTP Service by ensuring only authenticated users can make action on the HTTP API with mTLS by using certificats.
This will ensure that only the authorized entities can communicate with the HTTP API and can make action such as executing the PSPs.

Describe the solution you'd like
The solution would be to add this has a feature and enable this one by using a CLI flag like --mTLS for enabling the mTLS authentication. Maybe in the future, we can also add another authentification method like --PGP.
This would not be a mandatory flag and will be able to be turn on/off with only a simple CLI flags.

This is part of https://github.com/ethereum-optimism/security-pod/issues/158