[7.x] [Alerting] Add alert.updatedAt field to represent date of last user edit (#83784)

[ymao1]

Backports the following commits to 7.x:

• [Alerting] Add alert.updatedAt field to represent date of last user edit ([Alerting] Add alert.updatedAt field to represent date of last user edit #83784)

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: b7be6db

Metrics [docs]

Saved Objects .kibana field count

Every field in each saved object type adds overhead to Elasticsearch. Kibana needs to keep the total field count below Elasticsearch's default limit of 1000 fields. Only specify field mappings for the fields you wish to search on or query. See https://www.elastic.co/guide/en/kibana/master/development-plugin-saved-objects.html#_mappings

id	before	after	diff
alert	30	31	+1

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream