feat(measurexlite): generate HTTP traces (#881)

In a pure step-by-step model, we don't need to trace HTTP round trips like we did before. We _may_ want in the future to also have some form of HTTP tracing (see https://github.com/ooni/probe-cli/pull/868 for a prototype) but doing that is currently not in scope for moving forward the step-by-step design. For this reason, I only added a public convenience function for formatting an OONI spec compatible request. I also added new fields, which should be documented inside the ooni/spec repository (see https://github.com/ooni/probe/issues/2238).

Required by https://github.com/ooni/probe/issues/2237

internal/model/archival.go

@@ -193,6 +193,9 @@ type ArchivalTLSOrQUICHandshakeResult struct {
 //
 // See https://github.com/ooni/spec/blob/master/data-formats/df-001-httpt.md.
 type ArchivalHTTPRequestResult struct {
+	Network       string               `json:"network,omitempty"`
+	Address       string               `json:"address,omitempty"`
+	ALPN          string               `json:"alpn,omitempty"`
 	Failure       *string              `json:"failure"`
 	Request       ArchivalHTTPRequest  `json:"request"`
 	Response      ArchivalHTTPResponse `json:"response"`