Checks if the given text is present in the page source.
Returns true if it's present; false if otherwise.

*Example:*
| ${pageSource}= | 'Get Source' |
| ${isTextPresentInPageSource}= | Is Text Present In Page Source | ${pageSource} | foo bar |

=>

| ${isTextPresentInPageSource} = True   # or ${isTextPresentInPageSource} = False