Add term-level RRM settings

[nfmohit]

Feature Description

As part of RRM Phase 2, the WordPress taxonomy term screens will allow users to override the snippet configuration at the taxonomy term level. This issue should implement the fields to allow the said configuration.

Example mock:

The select field having a label of “Product ID Override”* will reflect and change the value of the googlesitekit_rrm_{Publication ID}:productID term meta setting with the following options:

1. “No change”*; Default; Value: Empty string.
2. “Off”*; Value: none.
3. “Open access”*; Value: openaccess.
4. Any available product IDs for the connected publication, obtainable using the new productIDs module setting.

* The final version of the labels should be checked and confirmed with Sigal and Mariya.

In order to add the field, the following WordPress hooks should be used:

• {$taxonomy}_add_form_fields
• {$taxonomy}_edit_form_fields

The following hooks should be used to handle the saving of the term meta setting:

• created_{$taxonomy}
• edited_{$taxonomy}

• See the relevant section in the design doc.

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Acceptance criteria

Implementation Brief

Test Coverage

QA Brief

Changelog entry