fix: template mg-exporter names with release fullname

[enys]

Template mg-exporter resource names with release-scoped fullnames in both memgraph and memgraph-high-availability charts, and update related selectors/references so multiple releases can coexist in the same namespace. Also validated with helm lint and helm template before and after the change.

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Tracking

• [Link to Epic/Issue] Non templated names for mg-exporter #233 (issue describes mg-exporter naming collision)

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✅ enys
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[enys]

Leaving this in draft for now, as I haven't run full validation yet.