Pull request: all: imp http handlers, imp docs

Merge in DNS/adguard-home from fix-openapi to master

Squashed commit of the following:

commit 0e7530472fb566e5cab73d178c8ec16e5ef11dcb
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed Jan 13 17:02:06 2021 +0300

    all: imp http handlers, imp docs

internal/home/auth_test.go

@@ -119,7 +119,7 @@ func TestAuthHTTP(t *testing.T) {
 	w.hdr = make(http.Header)
 	r := http.Request{}
 	r.Header = make(http.Header)
-	r.Method = "GET"
+	r.Method = http.MethodGet
 
 	// get / - we're redirected to login page
 	r.URL = &url.URL{Path: "/"}