* feat(tsdb): allow appending to ST capable XOR chunk optionally
Only for float samples as of now. Supports for in-order and out-of-order
samples.
Make sure that on readout the ST capable chunks are returned automatically.
When the chunks are returned as is, this is trivially true.
When a chunk needs to be re-coded due to deletion (tombstone) markers,
we take the encoding of the original chunk.
When a chunk needs to be created from overlapping chunks, we observe
whether ST is zero or not and create the new chunk based on that.
Signed-off-by: György Krajcsovits <gyorgy.krajcsovits@grafana.com>