Helm: Allow setting annotations for memberlist and query-scheduler-discovery services

[tabboud]

What this PR does / why we need it:
Both the memberlist and query-scheduler-discovery services do not provide a way to add annotations.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• Title matches the required conventional commits format, see here
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[CLAassistant]

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[tabboud]

The query-scheduler-discovery service is not technically the backend service, but given it's deployed along with it and currently uses the backendSelectorLabels, this seems appropriate to add these annotations as well.