Add option to toggle term counter

[MARQAS]

Description of the Change

This PR adds an option to enable/disable the term count option in the Instant results widget.

Closes #2610

How to test the Change

• By default the counter is enabled
• Go to ElasticPress features -> Instant results -> Disable the term count option
• Notice that the number of posts is disabled

Changelog Entry

Added - An option to toggle the term count in Instant results

Credits

Props @MARQAS

Checklist:

• [x] I agree to follow this project's Code of Conduct.
• [ ] I have updated the documentation accordingly.
• [ ] I have added tests to cover my change.
• [ ] All new and existing tests pass.