Ask the user before installing InfluxDB

[M3t4Data]

First of all, thank you for your work on this package.

Users who want to install Grafana are not made aware that InfluxDB is installed at the same time as the package (there's no mention of InfluxDB when the package is installed from Yunohost). Would it be possible to ask them before doing so (with a boolean for example) or at least to mention it ?