Add letter jobs page, client and test

app/notify_client/letter_jobs_client.py

@@ -0,0 +1,21 @@
+from app.notify_client import NotifyAdminAPIClient
+
+
+class LetterJobsClient(NotifyAdminAPIClient):
+
+    def __init__(self):
+        super().__init__("a", "b", "c")
+
+    def init_app(self, app):
+        self.base_url = app.config['API_HOST_NAME']
+        self.service_id = app.config['ADMIN_CLIENT_USER_NAME']
+        self.api_key = app.config['ADMIN_CLIENT_SECRET']
+
+    def get_letter_jobs(self):
+        return self.get(url='/letter-jobs')['data']
+
+    def send_letter_jobs(self, job_ids):
+        return self.post(
+            url='/send-letter-jobs',
+            data={"job_ids": job_ids}
+        )['data']