A tool which can be used to examine the content of sstable(s) and
execute various operations on them. The currently supported operations
are:
* dump - dumps the content of the sstable(s), similar to sstabledump;
* index-dump - dumps the content of the sstable index(es), similar to
scylla-sstable-index;
* writetime-histogram - generates a histogram of all the timestamps in
the sstable(s);
* custom - a hackable operation for the expert user (until scripting
support is implemented);
* validate - validate the content of the sstable(s) with the mutation
fragment stream validator, same as scrub in validate mode;
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