fix(metric_aggregation): Fix duplicate metrics registration

[shantanualsi]

What this PR does / why we need it:

Fixes duplicate metric registration in metric aggregation in pattern ingesters. I used promauto.With(reg) along with m.reg.MustRegister(... that resulted in duplicate registration

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
  • Note that Promtail is considered to be feature complete, and future development for logs collection will be in Grafana Alloy. As such, feat PRs are unlikely to be accepted unless a case can be made for the feature actually being a bug fix to existing behavior.
• Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
• If the change is deprecating or removing a configuration option, update the deprecated-config.yaml and deleted-config.yaml files respectively in the tools/deprecated-config-checker directory. Example PR

[ashwanthgoli]

lgtm

[loki-gh-app]

This PR must be merged before a backport PR will be created.