[NEW] How to Download Files and Data from your Linodes

[nmelehan]

This PR does a bunch of stuff. Prior to this PR, we had this guide:

Download a Local Copy of your Linode Backup
/docs/security/backups/download-backups-locally/

But, we didn't have a general "How to download files and data from your Linode" guide. This would be useful to have, both in general, and as a thing we could link to in our upcoming GDPR FAQ (as extracting your data from a cloud host is a concern under the GDPR). We do have this guide, but it's more targeted to someone who wants to make sure they have failsafe for the stuff on their Linode, instead of someone who just wants to get stuff out of Linode:

Backing Up Your Data
/docs/security/backups/backing-up-your-data/

The primary goal of this PR was the new 'How to Download Files and Data from your Linodes' guide. This topic shares a lot of overlap with the 'Download a Local Copy of your Linode Backup' guide, as those instructions are basically 1. Restore a backup -> 2. Download the stuff from the linode you restore to.

This PR puts the content from step 2 into a new shortguide called download-files-from-your-linode-shortguide, replaces that content from from 'Download a Local Copy of your Linode Backup' with the embedded shortguide, and then uses that shortguide in the new 'How to Download Files and Data from your Linodes'.

Those two guides were placed into a new /docs/security/data-portability/ section; the old location at /docs/security/backups/download-backups-locally/ was removed.

I also updated some other related guides and shortguides to make all of this make sense. When copy editing this PR, read through the guides in the next comment just to make sure they all make sense still, given the shifting around of content in the shortguides.

[nmelehan]

Guides affected by the shortguides that were edited or created:

/docs/security/data-portability/download-files-from-your-linode/
/docs/security/data-portability/download-backups-locally/
/docs/platform/disk-images/linode-backup-service/
/docs/databases/mysql/use-mysqldump-to-back-up-mysql-or-mariadb/
/docs/platform/disk-images/copying-a-disk-image-over-ssh/
/docs/tools-reference/file-transfer/filezilla/

Shortguides edited or created:

/docs/platform/disk-images/copy-disk-over-ssh-short/index.md
/docs/platform/disk-images/restore-backup-image-short/index.md
/docs/security/data-portability/download-files-from-your-linode-shortguide/index.md
/docs/tools-reference/file-transfer/filezilla-shortguide/index.md