[DOCS] Add missing anchors in cron expressions

Sections in this page are linked from Kibana UIs, so we should be explicit about the anchor IDs so they don't change and break links.

Related to elastic/kibana#58802

x-pack/docs/en/watcher/trigger/schedule/cron.asciidoc

@@ -16,6 +16,7 @@ WARNING:  While `cron` triggers are super powerful, we recommend using one of
           you want. You can use the <<croneval,`elasticsearch-croneval`>> tool to validate
           your cron expressions and see what the resulting trigger times will be.
 
+[[_cron_expressions]]
 ===== Cron expressions
 
 A cron expression is a string of the following form:
@@ -166,7 +167,7 @@ NOTE: Currently, you must specify `?` for either the `day_of_week` or
 | `0 5 9 LW * ?`        | Trigger at 9:05 AM on the last weekday of every month.
 |======
 
-
+[[_configuring_a_cron_schedule]]
 ===== Configuring a cron schedule
 
 To configure a `cron` schedule, you simply specify the cron expression as a
@@ -187,6 +188,7 @@ that triggers every day at noon:
 --------------------------------------------------
 // NOTCONSOLE
 
+[[_configuring_a_multiple_times_cron_schedule]]
 ===== Configuring a multiple times cron schedule
 
 To configure a `cron` schedule that triggers multiple times, you can