Rewrite of the entrypoint in Golang (#71)

- General improvements
    - Parallel download of only needed files at start
    - Prettier console output with all streams merged (openvpn, unbound, shadowsocks etc.)
    - Simplified Docker final image
    - Faster bootup
- DNS over TLS
    - Finer grain blocking at DNS level: malicious, ads and surveillance
    - Choose your DNS over TLS providers
    - Ability to use multiple DNS over TLS providers for DNS split horizon
    - Environment variables for DNS logging
    - DNS block lists needed are downloaded and built automatically at start, in parallel
- PIA
    - A random region is selected if the REGION parameter is left empty (thanks @rorph for your PR)
    - Routing and iptables adjusted so it can work as a Kubernetes pod sidecar (thanks @rorph for your PR)

internal/params/openvpn.go

@@ -0,0 +1,13 @@
+package params
+
+import (
+	libparams "github.com/qdm12/golibs/params"
+	"github.com/qdm12/private-internet-access-docker/internal/models"
+)
+
+// GetNetworkProtocol obtains the network protocol to use to connect to the
+// VPN servers from the environment variable PROTOCOL
+func (p *paramsReader) GetNetworkProtocol() (protocol models.NetworkProtocol, err error) {
+	s, err := p.envParams.GetValueIfInside("PROTOCOL", []string{"tcp", "udp"}, libparams.Default("udp"))
+	return models.NetworkProtocol(s), err
+}