Move moderation tool to a separate url

[akatsoulas]

The moderation tool should be moved to a separate URL and only specific groups should be able to access it.

[akatsoulas]

PR https://github.com/mozilla/kitsune/pull/6354

[akatsoulas]

Currently the URL is at /moderate

[emilghittasv]

I can confirm that:

• New questions submitted against freemium products end up inside the /moderate page list if the flagit-spam-autoflag and content_moderation waffle flags are enabled.
• New questions submitted against premium products don't end up inside the /moderate page.
• The "There is no content pending moderation." message is displayed if there are no flagged questions.
• The "View all deactivated users" button is visible and redirects the user to the /users/deactivation_log on click.
• The /moderate page is accessible only for users which have the flagit | flagged object| Can moderate flagged objects permission.
• Selecting a different topic from the "Change Topic" section will successfully change the topic associated with the question.
• The "View", "Edit" and "Delete" buttons are functional and no regressions encountered.
• The "Update Status" and "Update" buttons are functional an no regressions encountered.
• The question which was manually reported as misplaced will end up inside the /flagged list instead of /moderate.

During the verification of this ticket I've noticed that the question is removed from the /moderate page if manually flagged but not added back if the report was marked as invalid inside the /flagged page. (filled under https://github.com/mozilla/sumo/issues/2060)

Moving this ticket inside the release column.