Chore: [AEA-5803] - adopt new PSU secrets stack (#2511)

## Summary

- 🤖 Operational or Infrastructure Change

### Details

Step 2 of 3. PSU secrets have been created and populated, now to start
using them from the lambda

Co-authored-by: Connor Avery <[email protected]>

Author: tstephen-nhs

SAMtemplates/functions/main.yaml

@@ -431,9 +431,12 @@ Resources:
           LOG_LEVEL: !Ref LogLevel
           NHS_NOTIFY_PRESCRIPTIONS_SQS_QUEUE_URL: !Ref NHSNotifyPrescriptionsSQSQueueUrl
           TABLE_NAME: !Ref PrescriptionNotificationStatesTableName
-          API_KEY_SECRET: secrets-PSU-Notify-API-Key
-          PRIVATE_KEY_SECRET: secrets-PSU-Notify-PrivateKey
-          KID_SECRET: secrets-PSU-Notify-Application-KID
+          API_KEY_SECRET:
+            Fn::ImportValue: !Sub ${StackName}-PSU-Notify-API-Key
+          PRIVATE_KEY_SECRET:
+            Fn::ImportValue: !Sub ${StackName}-PSU-Notify-PrivateKey
+          KID_SECRET:
+            Fn::ImportValue: !Sub ${StackName}-PSU-Notify-KID
           NHS_NOTIFY_ROUTING_ID_PARAM: !Ref NotifyRoutingPlanIDParam
           NOTIFY_API_BASE_URL_PARAM: !Ref NotifyAPIBaseURLParam
           MAKE_REAL_NOTIFY_REQUESTS_PARAM: !Ref EnableNotificationsExternalParam
@@ -497,8 +500,10 @@ Resources:
         Variables:
           LOG_LEVEL: !Ref LogLevel
           TABLE_NAME: !Ref PrescriptionNotificationStatesTableName
-          APP_ID_SECRET: secrets-PSU-Notify-Application-ID
-          API_KEY_SECRET: secrets-PSU-Notify-API-Key
+          APP_ID_SECRET:
+            Fn::ImportValue: !Sub ${StackName}-PSU-Notify-Application-ID
+          API_KEY_SECRET:
+            Fn::ImportValue: !Sub ${StackName}-PSU-Notify-API-Key
     Metadata:
       BuildMethod: esbuild
       guard: