Support `stringlabels`

[jeschkies]

Prometheus has different label implementations. Its stringlabels can help Loki avoid allocation in its pipeline. This issue tracks the effort to migrate to the new Prometheus labels.Labels signature to enable support for stringlabels.

A prototype is available at https://github.com/jeschkies/loki/tree/karsten/stringlabels

Note: labels.Labels is not an interface. stringlabels are enabled with a build tag.

Tests

• ./pkg/analytics
• ./pkg/compactor
• ./pkg/distributor refactor(stringlabels): Support stringlabels distributor tests #17123
• ./pkg/indexgateway
• ./pkg/logqlanalyzer
• ./pkg/kafka refactor(stringlabels): Support stringlabels distributor tests #17123
• ./pkg/ingester
• ./pkg/loghttp
• ./pkg/ruler
• ./pkg/runtime
• ./pkg/storage
• ./pkg/pattern
• ./pkg/querier
• ./pkg/engine
• ./pkg/logproto
• ./pkg/logqlmodel
• ./pkg/queue
• ./pkg/chunkenc
• ./pkg/dataobj
• ./pkg/logql
• ./pkg/push

Production Code

• filter.FilterFunc
• log.StreamPipeline refactor(stringlabels): Support stringlabels in log.StreamPipeline #17216
• logproto.FromLabelAdaptersToLabels