Enable lint rules for Promise handling to discourage misuse of them. (#2607)

* Enable lint rules for Promise handling to discourage misuse of them.
Squashed all of Hugh's commits into one.

---------

Co-authored-by: Hugh Nimmo-Smith <hughns@element.io>

src/initializer.tsx

@@ -10,6 +10,7 @@ import { initReactI18next } from "react-i18next";
 import LanguageDetector from "i18next-browser-languagedetector";
 import Backend from "i18next-http-backend";
 import * as Sentry from "@sentry/react";
+import { logger } from "matrix-js-sdk/src/logger";
 
 import { getUrlParams } from "./UrlParams";
 import { Config } from "./config/Config";
@@ -73,6 +74,9 @@ export class Initializer {
           order: ["urlFragment", "navigator"],
           caches: [],
         },
+      })
+      .catch((e) => {
+        logger.error("Failed to initialize i18n", e);
       });
 
     // Custom Themeing
@@ -120,10 +124,15 @@ export class Initializer {
     // config
     if (this.loadStates.config === LoadState.None) {
       this.loadStates.config = LoadState.Loading;
-      Config.init().then(() => {
-        this.loadStates.config = LoadState.Loaded;
-        this.initStep(resolve);
-      });
+      Config.init().then(
+        () => {
+          this.loadStates.config = LoadState.Loaded;
+          this.initStep(resolve);
+        },
+        (e) => {
+          logger.error("Failed to load config", e);
+        },
+      );
     }
 
     //sentry (only initialize after the config is ready)