Initial changes for organization level activity page

What does this MR do and why?

As per #415300 (closed) this MR:

• adds a new activity route for organizations,
• adds new menu item under the manage
• prepares activities for the frontend part

Screenshots or screen recordings

Before	After

Without activities	With activities

How to set up and validate locally

1. Checkout the branch.
2. Access an organization with some projects/groups.
3. Visit the activity page (Organization/Activity).
4. Verify that activities are displayed properly, and confirm that you can use the filter as expected.

note: if you don't see organizations page, you might need to enable ui_for_organizations FF.

Related to #415300 (closed)