Add error handling to schedule coredns

[ryehowell]

Description

Fixes #221.

Adds additional check for existence of annotation on the coredns deployment prior to attempting to patch which is causing errors. This looks to be a change introduced with the EKS CoreDNS deployment where the annotation is no longer added by default.

Documentation

TODOs

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Please ensure all of these TODOs are completed before asking for a review.

• [ ] Ensure the branch is named correctly with the issue number. e.g: feature/new-vpc-endpoints-955 or bug/missing-count-param-434.
• [ ] Update the docs.
• [ ] Keep the changes backward compatible where possible.
• [ ] Run the pre-commit checks successfully.
• [ ] Run the relevant tests successfully.
• [ ] Ensure any 3rd party code adheres with our license policy or delete this line if its not applicable.

Release Notes (draft)

Added / Removed / Updated [X].

Migration Guide