Add `Usage by project` table to group data transfer dashboard

What does this MR do and why?

Related to #386406

We are starting to build a dashboard to monitor egress data transfer. The first dashboard will be at the group level in Settings -> Usage quotas.

This MR builds the "Usage by project" table.

Note: if you add up the data used by each project it might not match the total data used. This may be an API bug. I asked about it in !113392 (comment 1337457742)

Screenshots or screen recordings

Loading

Desktop	Mobile

Success

Desktop	Mobile

With pagination

Desktop	Mobile

Error

How to set up and validate locally

1. Enable the data_transfer_monitoring feature flag
   • bin/rails console
   • Feature.enable(:data_transfer_monitoring)
2. Seed the data
   • Open the console bin/rails console
   • Go to https://gitlab.com/-/snippets/2522604
   • Copy the class and paste it in the console
   • Find a group with some projects in it and make note of the group id (displayed on the overview page)
   • Run PopulateDataTransfer.run(<group_id>) in the console
   • Press q then type exit to get back to the normal command prompt
3. Navigate to a top level group -> Settings -> Usage quotas
4. Click on the Transfer tab

Testing pagination

Change app/assets/javascripts/api.js#L6 to 2.

MR acceptance checklist

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