Add form to set service broadcast account type

Note, no option at the moment to set the service broadcast account type
as None, or back to without the broadcast permission. This has been done
for speed of development given the chance of us needing this is very
low. We can add it later if we need to.

app/main/forms.py

@@ -2295,6 +2295,54 @@ class GoLiveNotesForm(StripWhitespaceForm):
     )
 
 
+class ServiceBroadcastAccountTypeField(GovukRadiosField):
+    # When receiving Python data, eg when instantiating the form object
+    # we want to convert it from a tuple of
+    # (service_mode, broadcast_channel, allowed_broadcast_provider)
+    # to a value to be used in our form such as "live-severe-ee"
+    def process_data(self, value):
+        (live, broadcast_channel, allowed_broadcast_provider) = value
+        account_type = None
+        if broadcast_channel:
+            account_type = "live" if live else "training"
+            account_type += f"-{broadcast_channel}"
+            if allowed_broadcast_provider:
+                account_type += f"-{allowed_broadcast_provider}"
+
+        self.data = account_type
+
+    # After validation we split the value back into its parts of service_mode
+    # broadcast_channel and provider_restriction to be used by the flask route to send to the
+    # API
+    def post_validate(self, form, validation_stopped):
+        if not validation_stopped:
+            split_values = self.data.split("-")
+            self.service_mode = split_values[0]
+            self.broadcast_channel = split_values[1]
+            self.provider_restriction = split_values[2] if len(split_values) == 3 else None
+
+
+class ServiceBroadcastAccountTypeForm(StripWhitespaceForm):
+    account_type = ServiceBroadcastAccountTypeField(
+        'Change cell broadcast service type',
+        thing='which type of account this cell broadcast service is',
+        choices=[
+            ("training-test-ee", "Training mode - EE network - Test channel only"),
+            ("training-test-o2", "Training mode - O2 network - Test channel only"),
+            ("training-test-three", "Training mode - Three network - Test channel only"),
+            ("training-test-vodafone", "Training mode - Vodafone network - Test channel only"),
+            ("training-severe", "Training mode - All networks - Public channel"),
+            ("live-test-ee", "Live - EE network - Test channel only"),
+            ("live-test-o2", "Live - O2 network - Test channel only"),
+            ("live-test-three", "Live - Three network - Test channel only"),
+            ("live-test-vodafone", "Live - Vodafone network - Test channel only"),
+            ("live-test", "Live - All networks - Test channel only"),
+            ("live-severe", "Live - All networks - Public channel"),
+        ],
+        validators=[DataRequired()]
+    )
+
+
 class AcceptAgreementForm(StripWhitespaceForm):
 
     @classmethod