cliccl/load: update load show with summary subcommand to display backup meta information

[jseldess]

PR: cockroachdb/cockroach#61131

From release notes:

Updated load show with summary subcommand to display meta information of an individual backup. Users are now able to inspect backup metadata, files, spans, and descriptors with the CLI command cockroach load show summary <backup_url> without a running cluster. [#61131][#61131]

[livlobo]

@kathancox - cockroach debug backup has superseded load show - so it does not need to be documented separately. Feel free to close. However, there might be information/context in the PRs for load show that might be useful for docs here.

[katmayb]

OK, I'll keep a note of this issue, but closing for tracking purposes.