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/settings/pia.go

@@ -0,0 +1,72 @@
+package settings
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/qdm12/private-internet-access-docker/internal/models"
+	"github.com/qdm12/private-internet-access-docker/internal/params"
+)
+
+// PIA contains the settings to connect to a PIA server
+type PIA struct {
+	User           string
+	Password       string
+	Encryption     models.PIAEncryption
+	Region         models.PIARegion
+	PortForwarding PortForwarding
+}
+
+// PortForwarding contains settings for port forwarding
+type PortForwarding struct {
+	Enabled  bool
+	Filepath models.Filepath
+}
+
+func (p *PortForwarding) String() string {
+	if p.Enabled {
+		return fmt.Sprintf("on, saved in %s", p.Filepath)
+	}
+	return "off"
+}
+
+func (p *PIA) String() string {
+	settingsList := []string{
+		"PIA settings:",
+		"Region: " + string(p.Region),
+		"Encryption: " + string(p.Encryption),
+		"Port forwarding: " + p.PortForwarding.String(),
+	}
+	return strings.Join(settingsList, "\n |--")
+}
+
+// GetPIASettings obtains PIA settings from environment variables using the params package.
+func GetPIASettings(params params.ParamsReader) (settings PIA, err error) {
+	settings.User, err = params.GetUser()
+	if err != nil {
+		return settings, err
+	}
+	settings.Password, err = params.GetPassword()
+	if err != nil {
+		return settings, err
+	}
+	settings.Encryption, err = params.GetPIAEncryption()
+	if err != nil {
+		return settings, err
+	}
+	settings.Region, err = params.GetPIARegion()
+	if err != nil {
+		return settings, err
+	}
+	settings.PortForwarding.Enabled, err = params.GetPortForwarding()
+	if err != nil {
+		return settings, err
+	}
+	if settings.PortForwarding.Enabled {
+		settings.PortForwarding.Filepath, err = params.GetPortForwardingStatusFilepath()
+		if err != nil {
+			return settings, err
+		}
+	}
+	return settings, nil
+}