Add number of chunk on process of synapse_auto_compressor

[rubo77]

It would be helpful to see the progress of synapse_auto_compressor when you run with a large -n option, e.g.

INFO  synapse_auto_compressor::manager] [1 of 10000] Running compressor on room !xyz:matrix.org with chunk size 500
INFO  synapse_auto_compressor::manager] [2 of 10000] Running compressor on room !abc:matrix.de with chunk size 500
...