feat: add high priority for cert-manager external-dns

[sonofgibs]

What problem does this PR solve?:
Update app configs to use DKP High PriorityClass for tools apps

Which issue(s) does this PR fix?:

https://d2iq.atlassian.net/browse/D2IQ-96663

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Checklist

• If the PR adds a version bump, ensure there is no breaking change in Licensing model (or NA).
• If a chart is changed or app configuration is significantly changed, the chart version is correctly incremented (so that apps are not automatically upgraded from a previous version of DKP).

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[coveralls]

Pull Request Test Coverage Report for Build 5017385546

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 79.532%

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Totals
Change from base Build 4945944319:	0.0%
Covered Lines:	136
Relevant Lines:	171

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💛 - Coveralls