ci(jenkins): Set GitHub notification context to apm-ci (#583)

Author: kuisathaverat

.ci/jobs/apm-agent-python-downstream.yml

@@ -15,6 +15,7 @@
         discover-pr-forks-trust: permission
         discover-pr-origin: merge-current
         discover-tags: false
+        notification-context: 'apm-ci/downstream'
         property-strategies:
             all-branches:
             - suppress-scm-triggering: true

.ci/jobs/apm-agent-python-mbp.yml

@@ -15,6 +15,7 @@
         discover-pr-forks-trust: permission
         discover-pr-origin: merge-current
         discover-tags: true
+        notification-context: 'apm-ci'
         repo: apm-agent-python
         repo-owner: elastic
         credentials-id: 2a9602aa-ab9f-4e52-baf3-b71ca88469c7-UserAndToken

.ci/jobs/apm-agent-python-mbp0.yml

@@ -15,6 +15,7 @@
         discover-pr-forks-trust: permission
         discover-pr-origin: merge-current
         discover-tags: false
+        notification-context: 'apm-ci/new'
         repo: apm-agent-python
         repo-owner: elastic
         credentials-id: 2a9602aa-ab9f-4e52-baf3-b71ca88469c7-UserAndToken