feat: use go1.16 and resources embedding (#235)

* feat: use go1.16 embedding for resources

We want to embed everything that can be easily embedded. We should, at a
minimum, replace the downloading of resources and bindata.

Ref: https://github.com/ooni/probe/issues/1367.

* fix: get rid of bindata and use go embed instead

* fix: start unbreaking some automatic tests

* fix: fetch resources as part of the mobile build

* fix: convert more stuff to go1.16

I still expect many breakages, but we'll fix them.

* fix: make the windows CI green

* fix: get resources before running QA

* fix: go1.16 uses modules by default

* hopefully fix all other outstanding issues

* fix(QA/telegram.py): add another DC IP address

* Apply suggestions from code review

internal/cmd/getresources/getresources.go

@@ -0,0 +1,51 @@
+// Command getresources downloads the resources
+package main
+
+import (
+	"crypto/sha256"
+	"errors"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"net/http"
+	"net/url"
+	"path/filepath"
+
+	"github.com/ooni/probe-cli/v3/internal/engine/resources"
+)
+
+func main() {
+	for name, ri := range resources.All {
+		if err := getit(name, &ri); err != nil {
+			log.Fatal(err)
+		}
+	}
+}
+
+func getit(name string, ri *resources.ResourceInfo) error {
+	workDir := filepath.Join("internal", "engine", "resourcesmanager")
+	URL, err := url.Parse(resources.BaseURL)
+	if err != nil {
+		return err
+	}
+	URL.Path = ri.URLPath
+	log.Println("fetching", URL.String())
+	resp, err := http.Get(URL.String())
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != 200 {
+		return errors.New("http request failed")
+	}
+	data, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		return err
+	}
+	checksum := fmt.Sprintf("%x", sha256.Sum256(data))
+	if checksum != ri.GzSHA256 {
+		return errors.New("sha256 mismatch")
+	}
+	fullpath := filepath.Join(workDir, name+".gz")
+	return ioutil.WriteFile(fullpath, data, 0644)
+}