Populate empty extension location status if necessary

[ianstanton]

When we install an extension that needs to be enabled with LOAD in Tembo Cloud, the cdb.status.extensions.locations info is empty. Example with auto_explain:

status:
  extensions:
  - description: administrative functions for PostgreSQL
    locations:
    - database: app
      enabled: false
      error: false
      schema: public
      version: "2.1"
    - database: postgres
      enabled: true
      error: false
      schema: pg_catalog
      version: "2.1"
    name: adminpack
  - description: The auto_explain module provides a means for logging execution plans
      of slow statements automatically, without having to run EXPLAIN by hand.
    locations: []
    name: auto_explain

This PR adds logic to populate default values for this case.