Abort on critical error during server startup (#8204)

Only a handful of critical errors are present in the codebase.
They all occur during server startup (in `app.StartServer()`).

Currently, when one of these critical error occurs, it is simpled
mentionned in the logs – then the error is discarded, and the app
attempts to continue the execution (and probably fails pretty quickly in
a weird way).

Rather than continuing operations in an unknow state, these errors should
trigger a clean exit.

This commit rewrites critical startup errors to be correctly
propagated, logged, and then terminate the command execution.
Additionnaly, it makes the server return a proper error code to the
shell.

cmd/platform/test.go

@@ -53,7 +53,11 @@ func webClientTestsCmdF(cmd *cobra.Command, args []string) error {
 	defer a.Shutdown()
 
 	utils.InitTranslations(a.Config().LocalizationSettings)
-	a.StartServer()
+	serverErr := a.StartServer()
+	if serverErr != nil {
+		return serverErr
+	}
+
 	api4.Init(a, a.Srv.Router, false)
 	api.Init(a, a.Srv.Router)
 	wsapi.Init(a, a.Srv.WebSocketRouter)
@@ -71,7 +75,11 @@ func serverForWebClientTestsCmdF(cmd *cobra.Command, args []string) error {
 	defer a.Shutdown()
 
 	utils.InitTranslations(a.Config().LocalizationSettings)
-	a.StartServer()
+	serverErr := a.StartServer()
+	if serverErr != nil {
+		return serverErr
+	}
+
 	api4.Init(a, a.Srv.Router, false)
 	api.Init(a, a.Srv.Router)
 	wsapi.Init(a, a.Srv.WebSocketRouter)