https://issues.rudder.io/issues/27153

Some cleaning-up in campaign code:

• use standard layout for CampaignEventState (case object/class in object CampaignEventState)
• create enums for query parameters in place of string: CampaignSortOrder, CampaignSortDirection
• factor out default value for CampaignSortOrder in pattern matching
• use the actual CampaignEventState in place of its string value in query
• remove MainCampaignService from CampaignHandler which is not used and create a dependency loop

Replaces #6424
Needed for https://github.com/Normation/rudder-plugins-private/pull/1038