Adding default templates for Metricbeat ECS data (#81744)

This PR adds four new templates that are automatically installed from the Monitoring plugin.

In 8.x, Metricbeat will be writing its data in ECS compliant format, even when used with xpack 
mode enabled (stack monitoring). In order to continue to support the legacy data format, new 
mappings have been created with the new ECS fields for indexing data, and alias fields for the 
legacy format which point to the corresponding ECS fields.

Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>
Co-authored-by: Mat Schaffer <mat@schaffer.me>

docs/reference/monitoring/indices.asciidoc

@@ -15,7 +15,7 @@ GET /_template/.monitoring-*
 By default, the template configures one shard and one replica for the
 monitoring indices. To override the default settings, add your own template:
 
-. Set the `template` pattern to `.monitoring-*`.
+. Set the `template` patterns to match existing `.monitoring-{product}-7-*` indices.
 . Set the template `order` to `1`. This ensures your template is
 applied after the default template, which has an order of 0.
 . Specify the `number_of_shards` and/or `number_of_replicas` in the `settings`
@@ -28,7 +28,7 @@ and the number of replicas to two.
 ----------------------------------
 PUT /_template/custom_monitoring
 {
-  "index_patterns": ".monitoring-*",
+  "index_patterns": [".monitoring-beats-7-*", ".monitoring-es-7-*", ".monitoring-kibana-7-*", ".monitoring-logstash-7-*"],
   "order": 1,
   "settings": {
     "number_of_shards": 5,