Add template as_timedelta (#22740)

source/_docs/configuration/templating.markdown

@@ -424,6 +424,17 @@ For example, if you wanted to select a field from `trigger` in an automation bas
 
    {% endraw %}
 
+- `as_timedelta(string)` converts a string to a timedelta object. Expects data in the format `DD HH:MM:SS.uuuuuu`, `DD HH:MM:SS,uuuuuu`, or as specified by ISO 8601 (e.g. `P4DT1H15M20S` which is equivalent to `4 1:15:20`) or PostgreSQL’s day-time interval format (e.g. `3 days 04:05:06`) This function can also be used as a filter.
+
+   {% raw %}
+
+   ```yaml
+   # Renders to "00:10:00" 
+   {{ as_timedelta("PT10M") }} 
+   ```
+
+   {% endraw %}
+
 - Filter `timestamp_local(default)` converts a UNIX timestamp to the ISO format string representation as date/time in your local timezone. If that fails, returns the `default` value, or if omitted the unprocessed input value. If a custom string format is needed in the string, use `timestamp_custom` instead.
 - Filter `timestamp_utc(default)` converts a UNIX timestamp to the ISO format string representation representation as date/time in UTC timezone. If that fails, returns the `default` value, or if omitted the unprocessed input value. If a custom string format is needed in the string, use `timestamp_custom` instead.
 - Filter `timestamp_custom(format_string, local=True, default)` converts an UNIX timestamp to its string representation based on a custom format, the use of a local timezone is default. If that fails, returns the `default` value, or if omitted the unprocessed input value. Supports the standard [Python time formatting options](https://docs.python.org/3/library/time.html#time.strftime).