Rephrase client owner sales opportunities as sprint checkup task.

This clarifies that the developer stories are explicitly meant to be used as food for thought while reflecting on new ways to create value for clients.

Note: A task has also been added to the sprint checklist to take some time thinking about ways we might anticipate the client's needs.

JIRA tickets: https://tasks.opencraft.com/browse/BIZ-1478

Discussions: https://forum.opencraft.com/t/sales-opportunity-developer-stories/1055