Fix WebHookEditor regression from jQuery removal

[yardenshoham]

Make these calls optional

• Fix Remove jQuery from the webhook editor #29211 (comment)

[wxiaoguang]

Maybe it's clearer to do so:

const httpMedhodInput = getElementById()
if (httpMedhodInput) {
    const updateContentType = () {
        httpMedhodInput.value == ...
    }
    httpMedhodInput.addEventListener(....)
}

[wxiaoguang]

Now, another JS error:

dom.js:9 Uncaught TypeError: Cannot read properties of undefined (reading 'length')
    at elementsCall (dom.js:9:17)
    at toggleElem (dom.js:44:3)
    at updateContentType (WebHookEditor.js:27:15)
    at initCompWebHookEditor (WebHookEditor.js:29:3)
    at HTMLDocument.<anonymous> (index.js:109:24)

Update: oops, rebuild JS (4d1ffda) and no error now. The errors only occur in 4af858f)