Refactor to Use oldObject from Events Instead of Managing shootsWithIssues Set

[petersutter]

What would you like to be added:

dashboard/backend/lib/watches/shoots.js

Line 13 in a330669

const { shootsWithIssues = new Set() } = options ?? {}

Currently, the module manually manages a shootsWithIssues set to track the unhealthy shoots. However, this can be simplified and made more efficient by leveraging the oldObject provided in the event handlers.

Using oldObject allows us to determine the previous state of the object and eliminates the need for an external tracking mechanism like shootsWithIssues.

Why is this needed: