Allow max length of user macros to 2048 (server side)

I would like to use user macro for host specific URL, which will be used in web monitoring template. This URL is long (~650chars) and it's truncated to 256 chars, what is limit for user macro. So I can't use user macro for web monitoring URL.

It'll be fine if you increase maximum length of user macro and it'll be same as maximum allowed length of URL (2048 chars). It make sense, if I can use user macro in monitored URL.