:sparkles: return set of issues when EKS Node Group is in degraded state

[stefanSpectro]

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What type of PR is this? /kind feature

What this PR does / why we need it:

We need this PR because when node groups go in to a degraded state no relevant information is returned to the user. This PR implements code that returns a set of health issues reported for the given node group so a user can have an understanding of what went wrong.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged): Fixes #

Special notes for your reviewer:

Checklist:

• [x] squashed commits
• [ ] includes documentation
• [ ] includes emojis
• [x] adds unit tests
• [ ] adds or updates e2e tests

Release note:

Return detailed error message to user when EKS NodeGroup goes in to a Degraded state