[Platform] Enhancement request for yb-admin list_snapshots and list_snapshot_schedules

[mheer9]

Description:
Currently to find the right snapshot needs two steps:

1. yb-admin list_snapshots show_details

... to get the snapshot for the namespace you want (I am assuming here that we do support snapshot schedules for more than one keyspace simultaneously).
... this output is going to be large as every table in the namespace is listed for each snapshot

2. yb-admin list_snapshot_schedules
   ... to cross reference the possible snapshot ids from 1 with their times.

Infrastructure: ALL

Feature Request:
The process of finding the right snapshot to restore needs to be streamlined - especially as this is a super critical activity, likely done at a time of stress for the admin and with major consequences if not done correctly.

Can we extend either:
1 to include the datetime of the snapshot; or
2 to include the namespace

(At the moment, with limited experience, I think 2 is sufficient).

[karlfunk-ydb]

I updated to remove hashes in the text, which zendesk was ok with but git uses as links..