Add a wrapping @context tag to JSON-LD generator (#454)

This patch is related to the [issue 386 of aas-specs]. We fix 
the JSON-LD generation so that the context can be served
directly at a given URL and digested in a JSON-LD document.

[issue 386 of aas-specs]: admin-shell-io/aas-specs#386

aas_core_codegen/jsonld/main.py

@@ -12,6 +12,7 @@
 This code has been originally developed by Fabien Amarger (murloc6),
 Elodie Thieblin (ethieblin), and Christian Glomb (wiresio).
 """
+
 import dataclasses
 import json
 from typing import (
@@ -382,7 +383,7 @@ def _generate(
     if len(errors) > 0:
         return None, errors
 
-    return Stripped(json.dumps(json_ld_context, indent=2)), None
+    return Stripped(json.dumps({"@context": json_ld_context}, indent=2)), None
 
 
 def execute(context: run.Context, stdout: TextIO, stderr: TextIO) -> int: