Fix openapi spec for required fields, switch to main as default branch

• Update Jenkinsfile to use main as default branch instead of master

• Add required properties to the openapi spec

spec/openapi.yaml

@@ -112,6 +112,12 @@ components:
   schemas:
     Country:
       type: object
+      additionalProperties: false
+      required:
+        - geoname_id
+        - iso_code
+        - names
+        - is_in_european_union
       properties:
         geoname_id:
           type: integer
@@ -134,6 +140,10 @@ components:
 
     City:
       type: object
+      additionalProperties: false
+      required:
+        - geoname_id
+        - names
       properties:
         geoname_id:
           type: integer
@@ -157,6 +167,10 @@ components:
 
     Error:
       type: object
+      additionalProperties: false
+      required:
+        - status_code
+        - message
       properties:
         status_code:
           type: integer