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/modify.go

@@ -0,0 +1,31 @@
+package pia
+
+import (
+	"fmt"
+	"net"
+	"strings"
+
+	"github.com/qdm12/private-internet-access-docker/internal/constants"
+)
+
+func (c *configurator) ModifyLines(lines []string, IPs []net.IP, port uint16) (modifiedLines []string) {
+	c.logger.Info("%s: adapting openvpn configuration for server IP addresses and port %d", logPrefix, port)
+	// Remove lines
+	for _, line := range lines {
+		if strings.Contains(line, "privateinternetaccess.com") ||
+			strings.Contains(line, "resolv-retry") {
+			continue
+		}
+		modifiedLines = append(modifiedLines, line)
+	}
+	// Add lines
+	for _, IP := range IPs {
+		modifiedLines = append(modifiedLines, fmt.Sprintf("remote %s %d", IP.String(), port))
+	}
+	modifiedLines = append(modifiedLines, "auth-user-pass "+string(constants.OpenVPNAuthConf))
+	modifiedLines = append(modifiedLines, "auth-retry nointeract")
+	modifiedLines = append(modifiedLines, "pull-filter ignore \"auth-token\"") // prevent auth failed loops
+	modifiedLines = append(modifiedLines, "user nonrootuser")
+	modifiedLines = append(modifiedLines, "mute-replay-warnings")
+	return modifiedLines
+}