Test Zstd compression

[cyriltovena]

From my understanding the ztsd decoder and encoder uses goroutines. This means when a decoder/encoder is pooled and will be garbage collected, but when release we don't call close and so we don't stop goroutines

We tried to add this finalizer https://github.com/grafana/loki/blob/main/pkg/chunkenc/pool.go#L235 from #3306 but we didn't for the encoder.

But I'm wondering if we should may be find another solution, possible this can cause go-routines leak even with a finalizer

• Investigate if the writer also need the same treatment example https://github.com/segmentio/kafka-go/blob/ea83b2934c4ff79c5e4795b0806062cab913b3ae/compress/zstd/zstd.go#L113
• Attempt to write better test or benchmark showing possible leak
• Test in a dev environment Ztsd and ensure goroutines count are looking normal.

Alternatively if there's still issues:

• Investigate if we can't refactor pooling to guarantee call to Close once release/GC. (May be use LRU / custom free list ?)
• Benchmark change if we do refactoring.

[kavirajk]

Adding few references that may be helpful!

1. Add zstd and flate compressions algorithms. #3064
2. https://grafana.slack.com/archives/CEPJRLQNL/p1635827026297100

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