No cache / time of last update not taken into account

### What Happened?

AppCenter looks for updates too often. That leads to an annyoing experience.

### Steps to Reproduce

1. Start AppCenter. Overview is showing the "Check for updates" spinner.
2. Wait for the task to complete.
3. Click the "update" icon: AppCenter starts to check for updates again, don't showing me the results of the last check. So I have to wait again.

This may be repeated for every start of the app.

### Expected Behavior

Only check for updates once upon a time and cache that result for 2 to 24 hours. Suggestions: 24h on stable, 8h on RC, even less (2h?) on daily.

### OS Version

8.x (Early Access)

### Session Type

Secure Session (Wayland)

### Software Version

Latest release (I have run all updates)

### Log Output

_No response_

### Hardware Info

_No response_