[STAR-2281] - Improve Client Briefing Template with included example.

This MR updates the client briefing template to make it more useful to client owners and bizdev, so that our relationships with clients can be more strategically considered. This includes both the structure and an example using a fictional client.

JIRA tickets: https://tasks.opencraft.com/browse/STAR-2281

Discussions: https://docs.google.com/document/d/1_EYAUBt8McNFrbrxidcisaEYpmygK7p-AzUYnfWyRTw/edit#