Update shared-autodiscover.asciidoc (#21827) (#22202)

add descriptions for default values of `labels.dedot` and `annotations.dedot`

(cherry picked from commit 601c323)

Co-authored-by: Peter Deng <newly.deng@gmail.com>

libbeat/docs/shared-autodiscover.asciidoc

@@ -170,9 +170,10 @@ If the `exclude_labels` config is added to the provider config, then the list of
 will be excluded from the event.
 
 if the `labels.dedot` config is set to be `true` in the provider config, then `.` in labels will be replaced with `_`.
+By default it is `true`.
 
 if the `annotations.dedot` config is set to be `true` in the provider config, then `.` in annotations will be replaced
-with `_`.
+with `_`. By default it is `true`.
 
 
 For example: