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/pia/parse.go

@@ -0,0 +1,54 @@
+package pia
+
+import (
+	"fmt"
+	"net"
+	"strconv"
+	"strings"
+
+	"github.com/qdm12/private-internet-access-docker/internal/constants"
+	"github.com/qdm12/private-internet-access-docker/internal/models"
+)
+
+func (c *configurator) ParseConfig(lines []string) (IPs []net.IP, port uint16, device models.VPNDevice, err error) {
+	c.logger.Info("%s: parsing openvpn configuration", logPrefix)
+	remoteLineFound := false
+	deviceLineFound := false
+	for _, line := range lines {
+		if strings.HasPrefix(line, "remote ") {
+			remoteLineFound = true
+			words := strings.Fields(line)
+			if len(words) != 3 {
+				return nil, 0, "", fmt.Errorf("line %q misses information", line)
+			}
+			host := words[1]
+			if err := c.verifyPort(words[2]); err != nil {
+				return nil, 0, "", fmt.Errorf("line %q has an invalid port: %w", line, err)
+			}
+			portUint64, _ := strconv.ParseUint(words[2], 10, 16)
+			port = uint16(portUint64)
+			IPs, err = c.lookupIP(host)
+			if err != nil {
+				return nil, 0, "", err
+			}
+		} else if strings.HasPrefix(line, "dev ") {
+			deviceLineFound = true
+			fields := strings.Fields(line)
+			if len(fields) != 2 {
+				return nil, 0, "", fmt.Errorf("line %q misses information", line)
+			}
+			device = models.VPNDevice(fields[1] + "0")
+			if device != constants.TUN && device != constants.TAP {
+				return nil, 0, "", fmt.Errorf("device %q is not valid", device)
+			}
+		}
+	}
+	if remoteLineFound && deviceLineFound {
+		c.logger.Info("%s: Found %d PIA server IP addresses, port %d and device %s", logPrefix, len(IPs), port, device)
+		return IPs, port, device, nil
+	} else if !remoteLineFound {
+		return nil, 0, "", fmt.Errorf("remote line not found in Openvpn configuration")
+	} else {
+		return nil, 0, "", fmt.Errorf("device line not found in Openvpn configuration")
+	}
+}