Store.InitFromEnvironment shall allow to specify another ENV VAR name

[nicoovh]

Is your feature request related to a problem? Please describe. When two tools are using configstore in a same ENV, their configuration may collide because the ENV var name is global.

Describe the solution you'd like The Store.InitFromEnvironnement shall have the VENV name as parameter, default to CONFIGURATION_FROM

Describe alternatives you've considered None

Additional context code location: https://github.com/ovh/configstore/blob/3cb5c15fa42274089080b7d976d6a19c3a9fa8e3/store.go#L48 related issue on utask: https://github.com/ovh/utask/issues/361