use custom http client instead of the http DefaultClient (#823)

This commit replaces the default client from the http lib with a custom one.
The previously used default client doesn't come with a timeout. This could cause
unwanted locks.
That solution chosen here creates a http client in the base component dendrite
with a constant timeout of 30 seconds. If it should be necessary to overwrite
this, we could include the timeout in the dendrite configuration.
Here it would be a good idea to extend the type "Address" by a timeout and
create an http client for each service.

Closes #820

Signed-off-by: Benedikt Bongartz <benne@klimlive.de>

Co-authored-by: Kegsay <kegan@matrix.org>

eduserver/api/input.go

@@ -15,6 +15,7 @@ package api
 
 import (
 	"context"
+	"errors"
 	"net/http"
 
 	commonHTTP "github.com/matrix-org/dendrite/common/http"
@@ -57,11 +58,11 @@ type EDUServerInputAPI interface {
 const EDUServerInputTypingEventPath = "/api/eduserver/input"
 
 // NewEDUServerInputAPIHTTP creates a EDUServerInputAPI implemented by talking to a HTTP POST API.
-func NewEDUServerInputAPIHTTP(eduServerURL string, httpClient *http.Client) EDUServerInputAPI {
+func NewEDUServerInputAPIHTTP(eduServerURL string, httpClient *http.Client) (EDUServerInputAPI, error) {
 	if httpClient == nil {
-		httpClient = http.DefaultClient
+		return nil, errors.New("NewTypingServerInputAPIHTTP: httpClient is <nil>")
 	}
-	return &httpEDUServerInputAPI{eduServerURL, httpClient}
+	return &httpEDUServerInputAPI{eduServerURL, httpClient}, nil
 }
 
 type httpEDUServerInputAPI struct {