Adds support for reporting indexing stats to the compare_run script

[seut]

Adds a new flag --report-indexing which causes the compare_run to show shards and shards segments statistical information.
Mostly useful when running index(write) benchmarks, reporting information about the resulting segments and shard flush, refresh and merge statistics.

Example output:

Shard indexing stats across all primary shards
 Segments
     |  cnt      avg_size      min_size      max_size 
  V1 |   44       7457.84       6064.00      19478.00
  V2 |   17       9926.06       6392.00      20300.00
    
 Flush                   
     |      Counts      |                   Times (ms)                
     | total   periodic |        sum        avg        min        max 
  V1 |     0          0 |       0.00       0.00       0.00       0.00
  V2 |     0          0 |       0.00       0.00       0.00       0.00 
    
 Refresh 
     |      Counts      |                   Times (ms)                
     | total    pending |        sum        avg        min        max 
  V1 |    88          0 | 9867992.00 2466998.22 2230420.00 2917457.00
  V2 |    61          0 | 15808759.00 3952189.95 3732926.00 4354724.00 
    
 Merge 
     |     Counts     |                   Times (ms)                |             Throttle Times (ms)             |      Docs       |     Bytes       | Throttle
     | total  current |        sum        avg        min        max |        sum        avg        min        max | total   current | total   current |    in MB
  V1 |     8        0 |     585.00     146.25     126.00     167.00 |       0.00       0.00       0.00       0.00 |  2028         0 | 504856         0 |    83.89
  V2 |     4        0 |     639.00     159.75     107.00     187.00 |       0.00       0.00       0.00       0.00 |  1418         0 | 265736         0 |    83.89 

[seut]

Still in draft as I recognized a huge variance when using the same branch for v1 and v2. Need to investigate/play around more to see how the variance can be decreased.