What this PR does / why we need it:
This PR comments out the metric_aggregation_enabled and metric_aggregation options in the loki-local-config.yaml file, as these configurations are not supported in Loki 3.1.2 and cause a parsing error when used.

Which issue(s) this PR fixes:
Fixes #15567

Special notes for your reviewer:

The commented-out configurations align the example configuration file with the behavior of Loki 3.1.2 to prevent confusion and errors for users attempting to use unsupported settings.

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