[v11.0.x] datatrails: only fetch metrics metadata when using the language provider, avoid redundant fetch of metric names

[grafana-delivery-bot[bot]]

Backport f93c330b66b0d3ab75c65680b745d7dd93efe51d from #87067

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What is this feature?

Previously, we called start on the language provider which also fetched an additional list of metric names. This is redundant, since we already have a mechanism for that fetch. Here, we only load the metadata, by using loadMetricsMetadata instead.

Special notes for your reviewer:

Please check that:

• [ ] It works as expected from a user's perspective.
• [ ] If this is a pre-GA feature, it is behind a feature toggle.
• [ ] The docs are updated, and if this is a notable improvement, it's added to our What's New doc.