New tool to bump current_versions.sh automatically

This commit contains a new utility that helps to automate a version bump
for sandbox.

You can run this command to get the vibe of what it does.

```
$ go run cmd/bump-version/main.go -help
```

In order to try it out you can run this command form sandbox root. By
default it won't overwrite anything. It will print to stdout a new
version of the current_versions.sh file where all the images are
calculate cloning the various repositories

```
$ go run cmd/bump-version/main.go
```

If you want to overwrite the current_versions file you can use the flag
`-overwrite`.

More will come but for now, that's the PoC. Ideally this can be hooked
to CI/CD and run periodically, opening a PR that can be evaluated and
merged.

Signed-off-by: Gianluca Arbezzano <gianarb92@gmail.com>

cmd/bump-version/git/git.go

@@ -0,0 +1,30 @@
+package git
+
+import (
+	g "github.com/go-git/go-git/v5"
+	"github.com/go-git/go-git/v5/storage/memory"
+)
+
+type Repository struct {
+	repo *g.Repository
+}
+
+func Clone(remote string) (*Repository, error) {
+	repo := &Repository{}
+	r, err := g.Clone(memory.NewStorage(), nil, &g.CloneOptions{
+		URL: remote,
+	})
+	if err != nil {
+		return nil, err
+	}
+	repo.repo = r
+	return repo, nil
+}
+
+func (r *Repository) GetHeadHash() (string, error) {
+	ref, err := r.repo.Head()
+	if err != nil {
+		return "", err
+	}
+	return ref.Hash().String(), nil
+}