Architecture: Ability to host multiple versions side-by-side

[orhtej2]

Describe the bug

Currently borg is hosted in /opt/borg-env, version being rebuilt on app upgrade. This means if I want to have multiple instances, once from master the other from testing the last one to install would 'win'.

Context

• Hardware: VPS bought online
• YunoHost version: 11.2.4
• I have access to my server: Through SSH
• Are you in a special context or did you perform some particular tweaking on your YunoHost instance?: no
• Using, or trying to install package version/branch: 1.1.16~ynh30
• If upgrading, current package version: n/a

Steps to reproduce

```sh
sudo yunohost app install borg
sudo yunohost app install https://github.com/YunoHost-Apps/borg_ynh/tree/testing
```

Expected behavior

2 instances, one from official release, the other from testing branch coexisting.

Logs

n/a