Add trigger selector for blueprint (#29598)

Co-authored-by: c0ffeeca7 <38767475+c0ffeeca7@users.noreply.github.com>

source/_docs/blueprint/selectors.markdown

@@ -52,6 +52,7 @@ The following selectors are currently available:
 - [Text selector](#text-selector)
 - [Theme selector](#theme-selector)
 - [Time selector](#time-selector)
+- [Trigger selector](#trigger-selector)
 
 Interactive demos of each of these selectors can be found on the
 [Home Assistant Design portal](https://design.home-assistant.io/#components/ha-selector).
@@ -1292,3 +1293,26 @@ time:
 
 The output of this selector will contain the time in 24-hour format,
 for example, `23:59:59`.
+
+## Trigger selector
+
+The triggers selector allows the user to input one or more triggers.
+On the user interface, the trigger part of the automation editor is shown.
+The value of the input contains a list of triggers.
+
+![Screenshot of an trigger selector](/images/blueprints/selector-trigger.png)
+
+This selector does not have any other options; therefore, it only has its key.
+
+```yaml
+trigger:
+```
+
+The output of this selector is a list of triggers. For example:
+
+```yaml
+# Example trigger selector output result
+- platform: numeric_state
+  entity_id: "sensor.outside_temperature"
+  below: 20
+```∏