[WIP] Partner::AGENCY_TYPES is an enum on Partners::Profile

[veezus]

Resolves #4241

Description

This PR converts Partner::AGENCY_TYPES from a constant on partner to an enum on Partners::Profile. It introduces a new agency_types_description method which accesses the value stored in the database.

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• Existing agency_type checks have been converted to agency_type_description
• Partner show / edit / update flow has been verified
• Existing specs around reporting still pass

Screenshots

Here's the data originally, migrated, rolled back, and migrated again:

[cielf]

@veezus Is this still a [WIP]?