Overwrite of gortr config file when upgrading from package

[edugas]

Hello,

When upgrading GoRTR to the latest version (gortr_0.14.7_amd64.deb), the package simply overwrites the existing config without asking (unlike OctorRPKI package asking to keep or overwrite the config).

I've only tested with the DEB package under Ubuntu 20.04 LTS.