[synthetics] Add maintenance windows options docs (#4035)

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Add maintenance windows options to synthetics docs. Relates to
elastic/synthetics#1103.

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---------

Co-authored-by: Mike Birnstiehl <[email protected]>

Author: emilioalvap

solutions/observability/synthetics/cli.md

@@ -180,6 +180,13 @@ If the journey contains external NPM packages other than the `@elastic/synthetic
 
     This can also be set in the configuration file using [the `monitor.fields` option](/solutions/observability/synthetics/configure-projects.md#synthetics-configuration-monitor). The value defined via the CLI will take precedence.
 
+`--maintenance-windows Array<string>`
+:   A list of maintenance window IDs used to associate every monitor with one or more [maintenance windows](/explore-analyze/alerts-cases/alerts/maintenance-windows.md). This argument accepts a variable number of values as shown in the example.
+
+        Example: `--maintenance-windows "maintenance-window-ID-1" "maintenance-window-ID-2`
+
+    This can also be set in the configuration file using [the `monitor.fields` option](/solutions/observability/synthetics/configure-projects.md#synthetics-configuration-monitor). The value defined via the CLI will take precedence.
+
 `--yes`
 :   The `push` command includes interactive prompts to prevent you from accidentally deleting or duplicating monitors. If running the CLI non-interactively, you can override these prompts using the `--yes` option. When the `--yes` option is passed to `push`:
 

solutions/observability/synthetics/configure-lightweight-monitors.md

@@ -377,6 +377,19 @@ $$$monitor-namespace$$$
     namespace: custom-namespace
     ```
 
+$$$monitor-maintenanceWindows$$$
+
+**`maintenance_windows`**
+:   Type: [string](/solutions/observability/synthetics/configure-lightweight-monitors.md#synthetics-lightweight-data-string)  
+
+    A list of maintenance window IDs used to associate this monitor with one or more [maintenance windows](/explore-analyze/alerts-cases/alerts/maintenance-windows.md).
+
+    **Examples**:
+
+    ```yaml
+    maintenance_windows: ["maintenance-window-ID-1", "maintenance-window-ID-2"]
+    ```
+
 ### HTTP options [synthetics-lightweight-http]
 
 The options described here configure Synthetics to connect via HTTP and optionally verify that the host returns the expected response.

solutions/observability/synthetics/configure-projects.md

@@ -295,6 +295,9 @@ For information on configuring monitors individually, refer to:
 * [Configure individual browser monitors](/solutions/observability/synthetics/configure-individual-browser-monitors.md) for browser monitors
 * [Configure lightweight monitors](/solutions/observability/synthetics/configure-lightweight-monitors.md) for lightweight monitors
 
+`maintenanceWindows` (`Array<string>`)
+:   A list of maintenance window IDs used to associate this monitor with one or more [maintenance windows](/explore-analyze/alerts-cases/alerts/maintenance-windows.md).
+
 ## `proxy` [synthetics-configuration-proxy]
 
 `uri` (`string`)