Get a list of admins for a set of gateway accounts

[stevenjmesser]

On a few occasions I've needed to communicate with administrators from a set of services. To do this, I've had to open many tabs, copy and paste email addresses into a spreadsheet, and then match up other information about the service with the email addresses.

As part of the Strong Customer Authentication work, we're going to need to engage with ~170 services, which means it could take a whole day to create the list. Similarly we don't have a good method of contacting all service administrators directly for regulatory or contractual changes; we rely on people picking up messages on cross-government Slack or elsewhere.

Over time, as the platform scales, we are likely to need to contact hundreds of services en masse, which cannot be done efficiently at the moment. It would be good to create a way to do this quickly and easily from Toolbox.