fix(MeshRetry): guard against multiple previous priorities

[johnharris85]

Checklist prior to review

Adds validation for the case where someone specifies OmitPreviousPriorities more than once. This wouldn't error today, but might result in unexpected behavior (we'll always just use the last one specified in the list).

• Link to relevant issue as well as docs and UI issues --
• This will not break child repos: it doesn't hardcode values (.e.g "kumahq" as a image registry) and it will work on Windows, system specific functions like syscall.Mkfifo have equivalent implementation on the other OS --
• Tests (Unit test, E2E tests, manual test on universal and k8s) --
• Do you need to update UPGRADE.md? --
• Does it need to be backported according to the backporting policy? --
• Do you need to explicitly set a > Changelog: entry here or add a ci/ label to run fewer/more tests?