feat: add inspect-repo executable

cmd/inspect-repo/main.go

+package main
+
+import (
+	"fmt"
+	"log"
+
+	"gitlab.com/juhani/go-semrel-gitlab/pkg/repo"
+)
+
+func main() {
+	r, err := repo.Inspect(".")
+	if err != nil {
+		log.Fatalln("Couldn't inspect repository", err)
+	}
+	fmt.Println(r.ReleaseNote())
+}