Update backreferences in string functions (#148)

Author: tothmano

apl/scalar-functions/string-functions.mdx

@@ -721,10 +721,10 @@ Backreferences match the same text as previously matched by a capturing group. W
 
 ```kusto
 ['github-issues-event']
-| project backreferences = replace_regex(@'observability=(\d+)', 'axiom=$1', creator)
+| project backreferences = replace_regex(@'observability=(.+)', 'axiom=$1', creator)
 ```
 
-[Run in Playground](https://play.axiom.co/axiom-play-qf1k/explorer?initForm=%7B%22apl%22%3A%22%5B'github-issues-event'%5D%5Cn%7C%20project%20backreferences%20%3D%20replace_regex%28%40'observability%3D%28%5Cd%2B%29'%2C%20'axiom%3D%241'%2C%20creator%29%22%7D)
+[Run in Playground](https://play.axiom.co/axiom-play-qf1k/explorer?initForm=%7B%22apl%22%3A%22%5B'github-issues-event'%5D%20%7C%20project%20backreferences%20%3D%20replace_regex(%40'observability%3D(.%2B)'%2C%20'axiom%3D%241'%2C%20creator)%22%7D)
 
 ## replace_string()