fix: add `lookup_value_regex` for taxonomy rest api

[rpenido]

Description

Configure the lookup_value_regex in the TaxonomyView. Currently, accessing the API using an invalid pk (i.e. using a str) throws an exception when the value is converted to int, returning status 500, instead of a 404.

Testing instructions

1. Please ensure that the tests cover the expected behavior of the view
2. Using this branch, run the dev server: python manage.py runserver
3. Create a superuser using python manage.py createsuperuser
4. Login in admin and authenticate with the user created (http://127.0.0.1:8000/admin)
5. In the same browser session, check the result in the API Viewer:
   • http://127.0.0.1:8000/tagging/rest_api/v1/taxonomies/invalid_pk (should return 404)

     ---

     Private-ref: FAL-3529

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[rpenido]

Thank you @ChrisChV!

@bradenmacdonald, could you do a CC review here?

[openedx-webhooks]

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