Trusted certificates handling

Current situation

Some users are using self-signed certificates for their domains. The orchestrator allows for this, but this is not documented (and the process differs for Python and Java plugins).

Desired outcome

A standard way to specify trusted certificates.

See https://tm-fr.doc.squashtest.com/v4/install-guide/installation-plugins/configurer-plugins-bt-outils-tiers.html#import-du-certificat-dans-la-jvm for hints.