Using environment values for actinia templates

[anikaweinmann]

Environment values should be able to be used inside actinia templates

• the environment depending values will be set via environment variables with the prefix TEMPLATE_VALUE_, then the plugin will use these values to set the values for the actinia module; e.g.
  • env variable: TEMPLATE_VALUE_DB_CONNECTION
  • and in the actinia module template {{ db_connection }}
  • the default env variable value can be overwritten by setting db_connection in the process chain of the actinia module
• by requesting an actinia module the plugin has to check if the parameter is set as environment variable. If yes:
  • change optional=True
  • add to description "default value exist for this installation"

Additional, fixing for GRASS GIS modules with only one parameter.

[mmacata]

Thanks! Cool! Just found a typo, else pls merge!