feat(feel): Add new built-in function is blank() (#4771)

* feat(feel): Add new built-in function `is blank()`

Add documentation for the new string built-in function `is blank()`.

* style: Auto-format

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

* remove i.e.

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: christinaausley <[email protected]>

Author: 3 people

docs/components/modeler/feel/builtin-functions/feel-built-in-functions-string.md

@@ -392,3 +392,28 @@ to base64(value: string): string
 to base64("FEEL")
 // "RkVFTA=="
 ```
+
+## is blank(string)
+
+<MarkerCamundaExtension></MarkerCamundaExtension>
+
+Returns `true` if the given string is blank (empty or contains only whitespaces).
+
+**Function signature**
+
+```feel
+is blank(string: string): boolean
+```
+
+**Examples**
+
+```feel
+is blank("")
+// true
+
+is blank(" ")
+// true
+
+is blank("hello world")
+// false
+```