Add instructions to download usage report for Codespaces

[2percentsilk]

Why:

Users have been confused on how to get more fine-grained information on their codespaces usage (see community/community#9611 as an example). The Export Data button is often overlooked and isn't currently surfaced in our docs.

Closes #13723

What's being changed:

In the Usage docs for Codespaces, we added a step at the end of the procedural on how to download a CSV of your usage data for an organization.
It follows the same pattern as the Actions Billing docs.

Check off the following:

• I have reviewed my changes in staging (look for "Automatically generated comment" and click Modified to view your latest changes).
• For content changes, I have completed the self-review checklist.

Writer impact (This section is for GitHub staff members only):

• This pull request impacts the contribution experience
  • I have added the 'writer impact' label
  • I have added a description and/or a video demo of the changes below (e.g. a "before and after video")

[github-actions]

Automatically generated comment ℹ️

This comment is automatically generated and will be overwritten every time changes are committed to this branch.

The table contains an overview of files in the content directory that have been changed in this pull request. It's provided to make it easy to review your changes on the staging site. Please note that changes to the data directory will not show up in this table.

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Content directory changes

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Source	Staging	Production	What Changed
content/billing/managing-billing-for-github-codespaces/viewing-your-codespaces-usage.md	Modified	Original

[ramyaparimi]

@2percentsilk
Thanks so much for opening a PR! I'll get this triaged for review ⚡

[hubwriter]

All good. 👍
I'll get this merged/published.
🚀

[github-actions]

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[shirafkanomid73-blip]

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