dispatch install should validate the image registry credentials

[neosab]

We should validate the user-specified image registry details in the install config. Otherwise, with an invalid registry, the installation is successful but creating functions could fail.

• [X] Bug
• [ ] Feature
• [ ] Enhancement

Detailed Description

Context

Possible Implementation

We can validate in the CLI but I would also prefer if this is done in the function manager as part of the driver initialization.

Complexity

• [X] Low - Simple enhancement or bug fix, no architectural changes or refactoring
• [ ] Medium - Change requires some thought, but is relatively isolated
• [ ] High - Significant architectural change or large refactor

Impact

• [X] Low - Annoyance, but does not impact business or functinality
• [ ] Medium - Issue can be worked around, but is causing pain
• [ ] High - Blocker

Your Environment

• Dispatch CLI version (or git commit):
• Dispatch Chart version (or image[s] tag):
• Operating System and version:
• Kubernetes version (and distribution):
• Etc (any other useful environmental information):

[berndtj]

Could we use the k8s readiness check for this? Though, I feel like it would be hard to relay the failure back to the user. We could introduce a "status" API and CLI which could relay the status of all the services with human readable error strings. This would probably also be good for general health monitoring.