ci: add configuration for posting to czo whenever CI fails in master.

Since notify is mostly depreciated  in the latest versions of CircleCI.
Although we can use use notify in CircleCI 2.0 but currently
there is no documentation regarding it.

We could have use notify here rather than this hacky solution but
if we use notify it was not possible to trigger CircleCI webhook only
for the main Zulip repository.

Also corrected the circle ci webhook for the case where we don't receive
previous in post request

.circleci/config.yml

@@ -140,6 +140,19 @@ aliases:
         ! sudo scripts/lib/upgrade-zulip-stage-2 2> >(tee upgrade.err >&2)
         grep -Fq 'upgrade-zulip-stage-2: Unsupported platform: ubuntu 16.04' upgrade.err
 
+  - &notify_failure_status
+    run:
+      name: On fail
+      when: on_fail
+      branches:
+        only: master
+      command: |
+        if [[ "$CIRCLE_REPOSITORY_URL" == 'git@github.com:zulip/zulip.git' ]]; then
+          curl  -H "Content-Type: application/json" \
+          -X POST -i 'https://chat.zulip.org/api/v1/external/circleci?api_key=$ZULIP_BOT_KEY&stream=automated%20testing&topic=master%20failing' \
+          -d '{"payload": { "branch": "'"$CIRCLE_BRANCH"'", "reponame": "'"$CIRCLE_PROJECT_REPONAME"'", "status": "failed", "build_url": "'"$CIRCLE_BUILD_URL"'", "username": "'"$CIRCLE_USERNAME"'"}}'
+        fi
+
 jobs:
   "bionic-backend-frontend-python3.6":
     docker:
@@ -184,6 +197,7 @@ jobs:
 
       - store_test_results:
             path: ./var/xunit-test-results/casper/
+      - *notify_failure_status
 
 
   "focal-backend-python3.8":
@@ -206,6 +220,7 @@ jobs:
         - *save_cache_requirements
         - *save_emoji_cache
         - *run_backend_tests
+        - *notify_failure_status
 
   "xenial-legacy":
     docker:
@@ -218,6 +233,7 @@ jobs:
 
       - *check_xenial_provision_error
       - *check_xenial_upgrade_error
+      - *notify_failure_status
 
   "bionic-production-build-python3.6":
     docker:
@@ -256,6 +272,7 @@ jobs:
             - production-install
             - production
             - production-extract-tarball
+      - *notify_failure_status
 
   "bionic-production-install-python3.6":
     docker:
@@ -277,6 +294,7 @@ jobs:
       - *restore_cache_package_json
       - *install_production
       - *save_cache_package_json
+      - *notify_failure_status
 
   "focal-production-install-python3.8":
     docker:
@@ -298,6 +316,7 @@ jobs:
       - *restore_cache_package_json
       - *install_production
       - *save_cache_package_json
+      - *notify_failure_status
 
 workflows:
   version: 2