headers: port from protocol

[kamilsk]

Motivation: propaganda will be used under the hood of protocol. It's a low-level package specific to HTTP.

Port from https://github.com/octolab/protocol/blob/e03a103e0484310d33e974f19222030607c3b11e/http/header/helpers.go

E.g.

	HeaderRequestID = "X-Request-Id"
	HeaderRoute     = "X-Route"
	HeaderSource    = "X-Source"
	HeaderTraceID   = "X-Trace-Id"

To do:

• add references where these headers are used, for example headers: add X-Request-UUID #7.