Add addActivity handler and createActivity method in HostService

- Implemented addActivity handler to create new activities with validation.
- Added createActivity method in HostService to handle activity creation logic.

serverless.yml

@@ -176,6 +176,22 @@ functions:
           path: /host/add-payment-details
           method: post
 
+  addActivity:
+    handler: src/modules/host/handlers/addActivity.handler
+    package:
+      patterns:
+        - 'src/modules/host/handlers/addActivity.*'
+        - 'src/modules/host/services/**'
+        - 'common/**'
+        - 'src/common/**'
+        - 'node_modules/@prisma/client/**'
+        - 'node_modules/.prisma/**'
+
+    events:
+      - httpApi:
+          path: /host/add-activity
+          method: post
+
   getHostById:
     handler: src/modules/host/handlers/getbyidhandler.handler
     package: