DAP-09: UI divviup-ts documentation still references now-gone `buckets` parameter for histogram metrics

[branlwyd]

See:

This was replaced by the length parameter. We should update our UI so that tasks created against the relevant versions of DAP show documentation referencing the length parameter rather than the buckets parameter.

[branlwyd]

While we're at it, the parameter is called chunkLength rather than chunk_length.