Define conditional transitions using JSON

[tomtitherington]

Background & Context*

Users should be able to define conditional transitions that will be evaluated before the transitions are called/executed. This means that users can create if statements/branches within their flows.

Goal*

We want to allow users to apply conditional logic and branching statements to their flows.

Implementation Details*

We need to first agree on the JSON schema/format for defining these conditions. I think we can use the SQL/JSON Path Language from Postgres. Here's a basic idea of how it could work.

Probably just best to create a custom JSONField for the TransitionSchema.condition field and then this serialization can be taken care of by the ModelViewSet.

Acceptance Criteria*

• Post the agreed JSON schema as a comment here. (We'll use this in the documentation)
• A REST API endpoint where a user can provide this definition for an associated TransitionSchema. This is okay if it's just on the ModelViewSet of the existing TransitionSchema view.
• This endpoint will create a new instance or update an existing one if necessary.

Dependencies

Blockers:

• An endpoint/view to update/create a TransitionSchema needs to exist before this work can be started.

*required field.