Optionally disable conversion variable in expression from string to numeric or boolean

[andrewtelnov]

In the most case it makes sense to convert string to numeric, if this conversion is doable. In this case expression will work with them as numeric when possible. For example, the expression: "{val1} + {val2}", where val1: "1" and val2: "2" will return 3.
However, in some cases developers need to have these variables as strings and want to have the result "12".
To support both scenarios, we are adding the following '#' variable prefix to disable the conversion.
"{val1} + {val2}" will return 3 and "{#val1} + {#val2}" will return "12".