Introduce commonly used built-in functions to JavaScript preprocessing and webhooks

Duktape library is used for Javascript preprocessing / webhooks, but Duktape object is removed (not available from JS). This removes built-in support of base64 encoding / decoding as well as the support of hex encoding / decoding (https://duktape.org/guide.html#builtin-duktape-enc).

I propose to introduce support of some commonly used functions like:

• base64encode
• base64decode
• md5
• ...

While it is possible to implement such functions in JS it is a bad approach requiring to copy-paste the same code chunk to preprocessing steps and webhook integrations.