Galexie: sub-command to report data quality, statistics of remote data storage

[chowbao]

Provide a sub-command such as ledgerexporter stats , which will inspect a remote data store and print to cli output a summary of the quality of data present on the store. Need to first identify the schema of the summary output , initial suggestions shown here, detecting ledger gaps is a key outcome that should be achieved:

=== Final Summary ===
Analysis took 300 seconds
DataStore: Type=GCS
DataStore Config: destination_bucket_path = "exporter-test/ledgers"

Total Ledgers: 34909
Total Partitions: 35
Oldest Ledger Sequence: 2
Newest Ledger Sequence: 50342
Schema:
  Ledgers Per File; 10
  Files Per Partition: 100

Ledger Gaps:
   400 - 550
   12320 - 12330

Invalid Partitions:
   300-399
   12300-12400

used lighthorizon's design for stats as a starting point for this feature.

Consider additional request parameter to narrow the remote data scanned by stats to report to only a specific partition prefix:

ledgerexporter stats --partition 300-399