Improve plugin documentation for file based configuration

[wass3rw3rk]

Description

The current (plugin) documentation doesn't mention the fact that most Vela maintained plugins also accept configuration (or parameters) via file. Tweak docs to call out ability to supply plugin configuration via file (where supported).

Value

Add clarity for plugin users on the different ways to provide plugin configuration.

Definition of Done

Documentation for supported plugins shows how to provide file based configuration.

Effort (Optional)

2 days

Impacted Personas (Optional)

Users