[FEATURE] drouting: custom column names

[hrant-ian]

Is your feature request related to a problem? Please describe.
No problem, just convenience and consistency across modules.

Describe the solution you'd like
Most modules, which target a database, allow the user to define custom column names. The drouting module only allows this for the dr_groups table. Would be awesome if this could also be supported for the dr_rules, dr_carriers and dr_gateways tables.

Implementation

• Component: drouting
• Type: module parameter
• Name: *_col

Describe alternatives you've considered
I've used views to translate between my own tables and the schema the drouting module expects.

Additional context

[hrant-ian]

Thanks @bogdan-iancu for adding this to the 3.1 milestone!