Tweak the User-Agent a bit (#1153)

* [bugfix] Use AccountDomain for user agent

By using the account domain we can pinpoint the source of the request
more accurately when looking at the User-Agent header.

* [chore] Align user-agent header with spec

Based on RFC 7231, our User-Agent header doesn't quite match. It seems
to always want Name [/ Version] pairs, with comments in parenthesis and
multiple comments separated by a semicolon.

Align our UA with that, using application name first by itself in case
someone has customised it with the source instance in a comment. Follow
that up with gotosocial/<version> and a comment pointing at the source
code.

This also drops the mention of gofed/activity since a fork is in use.

internal/transport/controller.go

@@ -59,7 +59,8 @@ type controller struct {
 // NewController returns an implementation of the Controller interface for creating new transports
 func NewController(db db.DB, federatingDB federatingdb.DB, clock pub.Clock, client pub.HttpClient) Controller {
 	applicationName := config.GetApplicationName()
-	host := config.GetHost()
+	host := config.GetAccountDomain()
+	proto := config.GetProtocol()
 	version := config.GetSoftwareVersion()
 
 	c := &controller{
@@ -69,7 +70,7 @@ func NewController(db db.DB, federatingDB federatingdb.DB, clock pub.Clock, clie
 		client:    client,
 		trspCache: cache.New[string, *transport](0, 100, 0),
 		badHosts:  cache.New[string, struct{}](0, 1000, 0),
-		userAgent: fmt.Sprintf("%s; %s (gofed/activity gotosocial-%s)", applicationName, host, version),
+		userAgent: fmt.Sprintf("%s (+%s://%s) gotosocial/%s", applicationName, proto, host, version),
 	}
 
 	// Transport cache has TTL=1hr freq=1min