feat!: enable structure metadata by default.

[slim-bean]

What this PR does / why we need it:

Structured metadata is require for native OTel ingestion and should be enabled by default, the catch is you need to be using v13 of the schema or newer for this to work.

This creates a bit of a tricky situation for us where we want this enabled by default in 3.0 but recognize a lot of folks may not have upgraded to the v13 schema.

This PR also includes a validation that if structured metadata is enabled, the active schema needs to be v13.

If it's not Loki will fail to start and give you instructions to disable structured metadata support, restart Loki and then upgrade the schema before attempting to re-enable this feature.

This approach is invasive but we think preferable to silently ingesting the structured metadata and discarding it becasue the storage schema doesn't know where to put it.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• CHANGELOG.md updated
  • If the change is worth mentioning in the release notes, add add-to-release-notes label
• Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
• For Helm chart changes bump the Helm chart version in production/helm/loki/Chart.yaml and update production/helm/loki/CHANGELOG.md and production/helm/loki/README.md. Example PR
• 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