Introduce PermissionSet Group Awaiter timeout

[packocz]

We've recently started running into intermittent delays of several hours in PSG updates. The recalculation post deploy (package upgrade really) can take more than 3hrs. The PSG Awaiter patiently blocks the subsequent update delaying feedback on our development.

PSG Awaiter should have a timeout (perhaps configurable) so that it would not sit around for so long and allow the rest of the deployment / upgrade process to proceed and potentially crash - given earlier feedback.

Further info from SF Support:

Further deployments should be possible even if PSG is still updating
The recalculation process can sometimes take longer due to dangling ForeignKeys. These can be removed by running specific fixers. If that is the case , developer support team from salesforce can help check further. As far as i understood as it is an Async process it might not have available resources to run

[alesremta-ext43767]

@dieffrei We've had a another tough week with this one. Are you still considering this as on option? Can I do something to help this along?

[packocz]

@dieffrei I tried to make a start here :-) Lemme know if I'm going in the right direction pls
#170