Add ExecReload= to the default systemd service

[Winterhuman]

Since v2.1.13, dnscrypt-proxy can be reloaded regardless of the hot reloading setting with SIGHUP, however, you can't use systemctl reload since the service file is missing an ExecReload entry. From what I understand, the service file is actually generated and not provided statically (somehow, not sure of the details), but, would it still be possible to include ExecReload in the default service file?

[welwood08]

I believe the change I suggest in #2957 should accomplish this but I'm unable to test it myself, feel free to give it a try.