Pricing: mention "build time" limit

[humitos]

We want to expose a "build time" limit in the pricing page.

This task will need also:

• Figure it out what's the correct number of minutes/hours
• https://ethicalads.metabaseapp.com/question/296-builds-by-day
• Expose "total build time" in the admin dashboard
• Show a simple progress bar
• Add an organization overview to understand what is the project consuming more build time
• Build a PoC in Metabase to play around with the display / concept
• Decide a soft limit for "build time"
• Contact organization that go over the soft limit
• Decide whether or not disable the organization if they go over that limit twice

Feel free to split this issue into multiple issues to be able to prioritize small tasks on each of the sprints.

[ericholscher]

I did an initial step here: readthedocs/ext-theme#566