(feat): added isPresent command to Element API

[AritraLeo]

I've added the isPresent() command as per the issue .
Although the code encountered a error in unit testing at - .navigateTo('https://duckduckgo.com')
line : 7 of duckDuckGo.js file.

I am mainly raising the PR to get my code reviewed to get a better understanding if I am moving in the right direction or not !

[CLAassistant]

All committers have signed the CLA.

[garg3133]

Closing this PR because the current solution is incorrect (it will always return true because the webElementOrId argument to isElementPresent will always be a WebElementPromise, which in turn is an instance of WebElement. So, element instanceof WebElement will always return true even if the element actually does not exist.

Also, as it turns out, the solution to this is not going to be simple and will take a lot more efforts to implement, so we'll be doing it ourselves.