changecontrol.v1: Add ChangeControlSummary model & service

Add a new ChangeControlSummary model that provides a lightweight
summary view of change controls, including:
 - Basic metadata (name, status, device_count, error, approved)
 - Action type counts
 - Timestamp tracking (created, edited, approved, scheduled, start, end)
 - User tracking for all state transitions

This ChangeControlSummary model enables efficient querying of change
control metadata without fetching the full ChangeControl info, which
contains heavy nested stage and action data.

Also add a new Creation type to track when and by whom a change control
was created, and add a creation field to the ChangeControl model to
store this information.

[GENERATED_COMMIT]

Change-Id: Iee69f8210284482c9edfaecb693516a33c90ec8c

Author: Arista Jenkins