JetBrains Central provider: support drawing credits from multiple orgs, like in Air

## Problem

In Air, user can select from which org to draw usage from if they have multiple orgs.

## Proposed solution

UI in 'Providers' to do so.

## Alternatives considered

It's actually possible to switch org using `central` CLI, but user needs to know about it.

## Additional context

Start in the Providers UI and inspect how the JetBrains Central provider currently handles organization selection and usage credits. Compare the requested behavior with Air and the existing central CLI org-switching flow. Done means users with multiple organizations can choose which organization supplies credits from the Providers UI.

Written by the indexing model from the issue text.