Auto config on install

[culmat]

Currently proxy comes with a generic default conf.
Allow installer to provide a custom shell / Powershell script to create a specific configuration.
The script is downloaded from an URL and executed.
Eventually set a default value based on DNS search suffix, COUNTRY environment variable etc, i.e. https://{DNS_SUFFIX}/rest/scriptrunner/latest/custom/proxyconf?country={COUNTRY}&user={USERNAME}
&environment={ENVIRONMENT}