Add function to load YAML files

This commit starts to remove some code redundancy from the startup
scripts for easier maintenance.

startup_scripts/startup_script_utils/__init__.py

@@ -0,0 +1 @@
+from .load_yaml import load_yaml

startup_scripts/startup_script_utils/load_yaml.py

@@ -0,0 +1,10 @@
+from ruamel.yaml import YAML
+from pathlib import Path
+
+def load_yaml(yaml_file: str):
+  yf = Path(yaml_file)
+  if not yf.is_file():
+    return None
+  with yf.open("r") as stream:
+    yaml = YAML(typ="safe")
+    return yaml.load(stream)