Create schema for plan processing status table

[Rkareko]

Create core.plan_processing_status with the following fields :-

Id id
Plan Id FK plan_id (nullable)
Event Id FK event_id (not null)
Template Id FK template_id (Points to core.templates.identifier) (not null)
Status status ( (null|initial - 0) | processing - 1 | complete 2)
Here we can store it as a Postgres Enum. Should be expressive but still efficient as ints.
Date_created date_created timestamp (only on insert)
Last_updated date_updated timestamp (insert, update record)