feat: custom-api's replaceAll with regex support

[ralphocdol]

{{ $description := "I think Ruth's dog1 is cuter than your dog2!" }}
<div><pre>Raw Data:   {{ $description }}</pre></div>
<div><pre>String:     {{ replaceAll "dog" "ferret" $description }}</pre></div>
<div><pre>Regex:      {{ replaceAll "dog\\d" "ferret" $description }}</pre></div>