Add editorial metadata analytics

[alecgeatches]

Description

This adds some VIP-only telemetry for editorial metadata fields:

• em_field_created, with data:
  • int term_id
  • string name
  • string slug
  • string type (e.g. text/checkbox)
• em_field_changed, with data (same as above):
  • int term_id
  • string name
  • string slug
  • string type (e.g. text/checkbox)
• em_field_deleted, with data (same as above):
  • int term_id
  • string name
  • string slug
  • string type (e.g. text/checkbox)

Additionally in #21 we also record these data related to EM fields:

• In record_add_custom_status(), which fires when a new custom status field is created, we record the number of users and number of required EM fields associated with that custom status.

• In record_update_custom_status(), which fires each time a custom status is edited in the Workflow editor, we record the number of users and number of required EM fields associated with that custom status.

Between these two sets of data, we should be able to see if folks are doing CRUD operations on EM fields as well as how many are being used in the required functionality of custom statuses.