Add Account metric "# active rails"

Add to the account details page, could look something like this:

This stat needs to be exposed on the `Account` entity on the subgraph level.

Would be nice to also add this as a column to the accounts list page.

Suggested by @SgtPooki

Start with the Account entity in the subgraph and trace how account data reaches the account details page. Then inspect the accounts list page to determine where a new column would fit. Done means the active-rails metric is exposed by the Account entity, displayed on the details page, and added to the list when appropriate.

Written by the indexing model from the issue text.