Add curl support

[blixten85]

Some trackers like MaM requires a script to run in order to update mam_id. The script uses curl and this needs to be installed on every update of GluetunVPN container.

It would be better if curl was already in the container as a standard, so I hereby request curl support for GluetunVPN.

[iridial]

well, the container has wget (as of version 3.40), you can see if you can make it work as required in a script.
I agree curl would be more convenient.