Add self-signing workflow to standalone exe export

Issue

Currently standalone executables generated by Enscape are blocked by ASR (attack surface reduction) rules in Windows Defender because they're not digitally signed.

Cause

Enscape won't sign executables created on a customer's machine (which is good security-wise).

Proposed Solution

Adding a configuration option (that can be deployed) which allows the specification of a certificate to sign the generated executables with would be an acceptable workaround.