Adding ImagePullPolicy config option to OSM Charms

Change-Id: I04ad8444088e8a360755dc4e22b7ea53942682b2
Signed-off-by: sousaedu <eduardo.sousa@canonical.com>
diff --git a/installers/charm/mon/config.yaml b/installers/charm/mon/config.yaml
index d06b68d..ee593ff 100644
--- a/installers/charm/mon/config.yaml
+++ b/installers/charm/mon/config.yaml
@@ -87,3 +87,9 @@
         name: name of the file for the certificate
         content: base64 content of the certificate
       The path for the files is /certs.
+  image_pull_policy:
+    type: string
+    description: |
+      ImagePullPolicy configuration for the pod.
+      Possible values: always, ifnotpresent, never
+    default: always
diff --git a/installers/charm/mon/src/charm.py b/installers/charm/mon/src/charm.py
index 8c0a6bc..1b7c74b 100755
--- a/installers/charm/mon/src/charm.py
+++ b/installers/charm/mon/src/charm.py
@@ -80,6 +80,7 @@
     grafana_user: str
     grafana_password: str
     certificates: Optional[str]
+    image_pull_policy: Optional[str]
 
     @validator("log_level")
     def validate_log_level(cls, v):
@@ -99,6 +100,18 @@
             raise ValueError("mongodb_uri is not properly formed")
         return v
 
+    @validator("image_pull_policy")
+    def validate_image_pull_policy(cls, v):
+        values = {
+            "always": "Always",
+            "ifnotpresent": "IfNotPresent",
+            "never": "Never",
+        }
+        v = v.lower()
+        if v not in values.keys():
+            raise ValueError("value must be always, ifnotpresent or never")
+        return values[v]
+
     @property
     def certificates_dict(cls):
         return _extract_certificates(cls.certificates) if cls.certificates else {}
@@ -167,7 +180,9 @@
         pod_spec_builder = PodSpecV3Builder()
 
         # Build Container
-        container_builder = ContainerV3Builder(self.app.name, image_info)
+        container_builder = ContainerV3Builder(
+            self.app.name, image_info, config.image_pull_policy
+        )
         certs_files = self._build_cert_files(config)
 
         if certs_files: