Free-trial mechanism for teams

[jldec]

We need a simple mechanism to offer free trials for teams which do not depend on using personal credits.
Let's ship a skateboard for this.

Breakdown

• Admin feature to grant credits to a team
• Show available credit balance in team billing settings
• Attribute workspace and prebuild usage to teams with available credits
• Communicate how to grant credits to a team - draft (internal)
• (nice to have) Update documentation (fix or remove 1st screenshot in team billing section).