docs: please add size requirements to kernel dump pages

[cpaelzer]

Carrying a comment in the forum suggesting useful content over here:
From: https://discourse.ubuntu.com/t/kernel-crash-dump/11575/9

Hi! As a possible point of improvement, I think it would be helpful to try to answer the question of how much disk space should be available on a system to house a full crash dump. Ostensibly that answer would be “as much RAM as is on the system”, but there’s also the defaults that are used for consideration (#MAKEDUMP_ARGS="-c -d 31" - compression and in-use-only pages).

It might also be useful to make mention of the ability to add NFS/FTP/SSH info into /etc/default/kdump-tools for saving dumps to remote locations!

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Reported from: https://documentation.ubuntu.com/server/how-to/software/kernel-crash-dump/

[cpaelzer]

@s-makin IMHO this would qualify for an ODA contributor, hence a ping as FYI