Enables adding a section `plugin.<plugin id>` and key/value to
Grafana configuration file which will be converted and sent
as environment variables to the backend plugin.
Also sends some additional environment variables, Grafana
version (GF_VERSION), Grafana edition (GF_EDITION) and
enterprise license path (GF_ENTERPRISE_LICENSE_PATH).
Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>
Fixes#21515,
