Add dendrite-upgrade-test (#1901)

* Add WIP binary for testing dendrite version upgrades

* WIP dendrite upgrade work

* Finish dendrite upgrade checks

* go mod tidy

* Review comments; print container logs on failure

* Linting

cmd/dendrite-upgrade-tests/tar.go

@@ -0,0 +1,57 @@
+package main
+
+import (
+	"archive/tar"
+	"compress/gzip"
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// From https://gist.github.com/mimoo/25fc9716e0f1353791f5908f94d6e726
+// Modified to strip off top-level when compressing
+func compress(src string, buf io.Writer) error {
+	// tar > gzip > buf
+	zr := gzip.NewWriter(buf)
+	tw := tar.NewWriter(zr)
+
+	// walk through every file in the folder
+	_ = filepath.Walk(src, func(file string, fi os.FileInfo, e error) error {
+		// generate tar header
+		header, err := tar.FileInfoHeader(fi, file)
+		if err != nil {
+			return err
+		}
+
+		// must provide real name
+		// (see https://golang.org/src/archive/tar/common.go?#L626)
+		header.Name = strings.TrimPrefix(filepath.ToSlash(file), src+"/")
+		// write header
+		if err := tw.WriteHeader(header); err != nil {
+			return err
+		}
+		// if not a dir, write file content
+		if !fi.IsDir() {
+			data, err := os.Open(file)
+			if err != nil {
+				return err
+			}
+			if _, err := io.Copy(tw, data); err != nil {
+				return err
+			}
+		}
+		return nil
+	})
+
+	// produce tar
+	if err := tw.Close(); err != nil {
+		return err
+	}
+	// produce gzip
+	if err := zr.Close(); err != nil {
+		return err
+	}
+	//
+	return nil
+}