Add new PROJECT_CREATE permission

Introduce a new `PROJECT_CREATE` permission and add it to the
ServiceAdministrator role.

This permission will be used to control access to project
creation, including visibility of a "Create project" button
in the Staff Area and access to a project creation form.

The button and form will be added in subsequent work.

Author: KatieB5

jobserver/authorization/permissions.py

@@ -20,6 +20,7 @@ class Permission(StrEnum):
 
     ORG_CREATE = auto()
 
+    PROJECT_CREATE = auto()
     PROJECT_MANAGE = auto()
 
     RELEASE_FILE_DELETE = auto()

jobserver/authorization/roles.py

@@ -31,6 +31,7 @@ class ServiceAdministrator:
     ]
     permissions = [
         Permission.USER_EDIT_PROJECT_ROLES,
+        Permission.PROJECT_CREATE,
     ]