[#170] Support .tar/.tgz unpacking during upload

During upload if X-Explode-Archive is set, gate tries to read archive and create an object for each file.
Each object acquires a FilePath attribute which is calculated relative to the archive root.
Archive could have compression via Gzip if "Content-Encoding: gzip" header is specified

Signed-off-by: Nikita Zinkevich <n.zinkevich@yadro.com>

internal/handler/utils.go

@@ -101,6 +101,13 @@ func newAddress(cnr cid.ID, obj oid.ID) oid.Address {
 	return addr
 }
 
+// setIfNotExist sets key value to map if key is not present yet.
+func setIfNotExist(m map[string]string, key, value string) {
+	if _, ok := m[key]; !ok {
+		m[key] = value
+	}
+}
+
 func ResponseError(r *fasthttp.RequestCtx, msg string, code int) {
 	r.Error(msg+"\n", code)
 }