NoCache middlewares should not remove preconditions from request

NoCache middleware [removes](https://github.com/go-chi/chi/blob/master/middleware/nocache.go#L42) preconditions from request but describes itself as cache disabling middleware. According to https://www.rfc-editor.org/rfc/rfc7232 preconditions may be used for protection against lost updates even when no caching is enabled for resource.

NoCache middleware should touch only response headers not request headers probably and should not block headers required for conditional requests to work.

Start in middleware/nocache.go at the linked line and read the RFC 7232 discussion of preconditions. Verify which request and response headers the middleware changes; done means conditional request preconditions remain available while cache-disabling response behavior is preserved.

Written by the indexing model from the issue text.