[Fleet] Implement preconditions in packages install state machine (#1…

…90986)

Closes #189353

## Summary

Small change that implements a precondition function for package install
state machine. This is needed for the subsequent work planned in
#169147.

Note that this code is added and tested, but it's not currently used and
it will actually be used only when
#175597 will be implemented.


### Checklist
- [ ] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios

Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>