Fix validation error for ImagePullPolicy in charms

Change-Id: I00711202fdbacd73e9205dd3fc34424893440be5
Signed-off-by: sousaedu <eduardo.sousa@canonical.com>
diff --git a/installers/charm/ro/src/charm.py b/installers/charm/ro/src/charm.py
index 5212393..9b2934f 100755
--- a/installers/charm/ro/src/charm.py
+++ b/installers/charm/ro/src/charm.py
@@ -73,7 +73,7 @@
     ro_database: str
     openmano_tenant: str
     certificates: Optional[str]
-    image_pull_policy: Optional[str]
+    image_pull_policy: str
 
     @validator("log_level")
     def validate_log_level(cls, v):