Enhancement: Changing tax_query field to term_id

[ovidiul]

This PR changes the field from the tax_query defined in ProductTag class, so it's compatible with the core definition of WP_Query taxonomy parameters.

The field possible values are term_id, name, slug or term_taxonomy_id. The default value is term_id.

Fixes #6584

Testing

1. Create a page and add a Products by Tag block.
2. Check that is rendered correctly in the editor.
3. Save the page and check that is rendered correctly in the frontend.

Performance Impact

Should be none, since the query already defaults to term_id by default

Changelog

Enhancement: Replace the ProductTag tax_query field to be the term_id instead of the id.