Change the "Unapproved" filter to count entries without the is_approved meta as well

[omarkasem]

Copied from https://github.com/GravityKit/GravityImport/issues/468

Steps to reproduce

With GravityView inactive, submit one entry in a form
Enable GravityView
Check the Unapproved filter, the entry will not be listed there
The filter only counts entries containing the is_approved meta with a value of 3.

This affects entries imported with GravityImport. When importing new entries using GravityImport, the is_approved entry meta is not created unless the user's CSV explicitly provides and maps a column for it.

This may cause confusion for users because the Unapproved counter in the Gravity Forms entries interface does not work as expected if the approval meta is missing:

The current solution when importing entries with GravityImport is to require the customer to manually add an approval status column to their CSV or use the gravityview/import/entry/created hook to set the approval meta.

However, that's not intuitive and it doesn't sound right to require customers to add entry meta for unapproved entries to make our approval system work as expected. They don't need to do this when submitting a form.

Slack discussion:
https://gravitykit.slack.com/archives/C727B06MB/p1722947461675509