Proxy setup only working with nessus

[de-jcup]

Situation

We have the class ProxyConfig which is extended for all adapter configurations in SecHub. While doing changes for #797 it become clear that the current situation is as following:

• Only adapters have currently a proxy support via TrustAll
• But none of the adapters config builders does call at least setProxyHostname - except the Nessus Adapter (which is deprecated)!
• It is also no part of the PDS default parameters!

As a sum up:
The proxy settings can currently not work (except Nessus) where it can be defined by system properties (or env entries) via

sechub.adapter.nessus.proxy.hostname
sechub.adapter.nessus.proxy.port

Wanted

The proxy handling shall be consistent

Solution

Introduce single spring value and use it inside every executor

sechub.adapter.proxy.hostname
sechub.adapter.proxy.port

like done for Nessus executor (but replace nessus variant with this as well) for every executor.