Refactor kafka to pure Go (franz-go), fix DBC stubs, update Dockerfile

pkg/can-go/internal/identifiers/char.go

@@ -0,0 +1,9 @@
+package identifiers
+
+func IsAlphaChar(r rune) bool {
+	return ('A' <= r && r <= 'Z') || ('a' <= r && r <= 'z')
+}
+
+func IsNumChar(r rune) bool {
+	return '0' <= r && r <= '9'
+}