add deprecated message in omnibus build for macos pipeline

Author: sabrina-datadog

tasks/omnibus.py

@@ -183,6 +183,7 @@ def build(
     skip_deps=False,
     skip_sign=False,
     major_version='7',
+    release_version="nightly",
     hardened_runtime=False,
     system_probe_bin=None,
     go_mod_cache=None,
@@ -197,6 +198,9 @@ def build(
     Build the Agent packages with Omnibus Installer.
     """
 
+    if release_version:
+        print("The release_version argument is deprecated and will be removed soon.")
+
     flavor = AgentFlavor[flavor]
     fips_mode = flavor.is_fips()
     durations = {}