Fix backup disk driver configuration for S3 support

[ArturoSirvent]

Fixes #14057

Summary

• Fix the backup disk in config/filesystems.php to use a dedicated BACKUP_FILESYSTEM_DRIVER env var instead of PRIVATE_FILESYSTEM_DISK
• Add AWS credential fields to the backup disk config so S3 backups work
• Use BACKUP_FILESYSTEM_ROOT with safe default (storage_path('app')) for backward compatibility
• Document BACKUP_FILESYSTEM_DRIVER and BACKUP_FILESYSTEM_ROOT in .env.example

Problem

The current backup disk config uses PRIVATE_FILESYSTEM_DISK as its driver value:

'backup' => [
'driver' => env('PRIVATE_FILESYSTEM_DISK', 'local'),
'root' => storage_path('app'),
],

This can lead to "s3_private" as the driver which is not valid (should be "s3")

[snipe]

Hi there - thanks for this! Can you please re-target this PR to point to the develop branch, per our Contributing documentation?

You don't usually need to close and re-open. After you create a pull request, you can modify the base branch so that the changes in the pull request are compared against a different branch. By changing the base branch of your original pull request rather than opening a new one with the correct base branch, you’ll be able to keep valuable work and discussion.

If you change that branch and you see bunch of someone else's commits in the "files changed" tab of this PR, you might need to rebase. (Leaving those changes in can make it kinda confusing to see this PR actually changes.)

To Rebase

Assuming you started with this repo as the origin, and added yourself as a named remote:

git fetch origin; git rebase origin/develop

otherwise git fetch whatever your remote is.

Thanks!

[snipe]

Hi there - thanks for this! Can you please re-target this PR to point to the develop branch, per our Contributing documentation?

You don't usually need to close and re-open. After you create a pull request, you can modify the base branch so that the changes in the pull request are compared against a different branch. By changing the base branch of your original pull request rather than opening a new one with the correct base branch, you’ll be able to keep valuable work and discussion.

If you change that branch and you see bunch of someone else's commits in the "files changed" tab of this PR, you might need to rebase. (Leaving those changes in can make it kinda confusing to see this PR actually changes.)

To Rebase

Assuming you started with this repo as the origin, and added yourself as a named remote:

git fetch origin; git rebase origin/develop

otherwise git fetch whatever your remote is.

Thanks!

[snipe]

Gentle ping :)

[codacy-production]

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