Is it possible to configure a CS:GO server so that in the first round everyone is is forced to use knifes only (no pistols)?
If so, how?
Try a plug in, a good place to find or request for plug ins is http://forums.alliedmods.net
Alliedmodders have great plugins for source engines.
The only way this is possible would be to use a plugin. Plugins can modify what is and isn't allowed on servers, so, for example, you could have someone freeze in their spot if they equip a gun on round one.
However, most likely nobody made a plugin for what you want yet, but if you make an account on these forums, and request a plugin, hopefully somebody can make a plugin suiting your needs.