Fix missing installed custom modules after upgrading

[Thovi98]

Problem

After each upgrade, all custom modules were removed.

Solution

Add a command which restore this directory

PR Status

• [x] Code finished and ready to be reviewed/tested
• [x] The fix/enhancement were manually tested (if applicable)

Automatic tests

Automatic tests can be triggered on https://ci-apps-dev.yunohost.org/ after creating the PR, by commenting "!testme", "!gogogadgetoci" or "By the power of systemd, I invoke The Great App CI to test this Pull Request!". (N.B. : for this to work you need to be a member of the Yunohost-Apps organization)

[Thovi98]

Mmh no didn't work, I will try to dig into it later

[Thovi98]

Tested and works !

[Thovi98]

Added during the V2 migration