[8.6] [DOCS] Adds email notifications setting (#147660) (#148690)

# Backport

This will backport the following commits from `main` to `8.6`:
- [[DOCS] Adds email notifications setting
(#147660)](#147660)

<!--- Backport version: 8.9.7 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sqren/backport)

<!--BACKPORT [{"author":{"name":"Lisa
Cawley","email":"lcawley@elastic.co"},"sourceCommit":{"committedDate":"2023-01-10T22:24:15Z","message":"[DOCS]
Adds email notifications setting
(#147660)","sha":"e6f57ba2c076926136b97fc82a75361762eaf1cf","branchLabelMapping":{"^v8.7.0$":"main","^v(\\d+).(\\d+).\\d+$":"$1.$2"}},"sourcePullRequest":{"labels":["Team:Core","Team:AppServicesSv","release_note:skip","docs","v8.7.0","v8.6.1"],"number":147660,"url":"https://github.com/elastic/kibana/pull/147660","mergeCommit":{"message":"[DOCS]
Adds email notifications setting
(#147660)","sha":"e6f57ba2c076926136b97fc82a75361762eaf1cf"}},"sourceBranch":"main","suggestedTargetBranches":["8.6"],"targetPullRequestStates":[{"branch":"main","label":"v8.7.0","labelRegex":"^v8.7.0$","isSourceBranch":true,"state":"MERGED","url":"https://github.com/elastic/kibana/pull/147660","number":147660,"mergeCommit":{"message":"[DOCS]
Adds email notifications setting
(#147660)","sha":"e6f57ba2c076926136b97fc82a75361762eaf1cf"}},{"branch":"8.6","label":"v8.6.1","labelRegex":"^v(\\d+).(\\d+).\\d+$","isSourceBranch":false,"state":"NOT_CREATED"}]}]
BACKPORT-->

Co-authored-by: Lisa Cawley <lcawley@elastic.co>

docs/setup/settings.asciidoc

@@ -325,6 +325,10 @@ experimental[] Indicates which roles to configure the {kib} process with, which
 run {kib} in different modes. Valid options are `background_tasks` and `ui`,
 or `*` to select all roles. *Default: `*`*
 
+`notifications.connectors.default.email`::
+Specifies the name of the connector that is used to send email notifications.
+In {ecloud}, the default value is `elastic-cloud-email`.
+
 [[path-data]] `path.data`::
 The path where {kib} stores persistent data
 not saved in {es}. *Default: `data`*