Testing: Use sftp.app group from 4.2 to manage sftp access, + fix permissions

[alexAubin]

Problem

• upcoming 4.2 will break sftp access
• no chmod o-rwx on $final_path

Solution

• Add the system user to sftp.app when relevant
• Fix $final_path's permissions

PR Status

• [X] Code finished.
• [ ] Tested with Package_check.
• [ ] Fix or enhancement tested.
• [ ] Upgrade from last version tested.
• [ ] Can be reviewed and tested.

Package_check results

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• An automatic package_check will be launch at https://ci-apps-dev.yunohost.org/, when you add a specific comment to your Pull Request: "!testme", "!gogogadgetoci" or "By the power of systemd, I invoke The Great App CI to test this Pull Request!"*

[ericgaspar]

!testme

[yunohost-bot]

:rocket:

[alexAubin]

(Test's gonna fail because it requires yunohost >= 4.2.3)

[alexAubin]

!testme

[yunohost-bot]

:carousel_horse:

[alexAubin]

!testme

[yunohost-bot]

:stuck_out_tongue_winking_eye:

[alexAubin]

!testme

[yunohost-bot]

Alrighty!