Merge 4.0.3 into release-4.1 (#7169)

* fix dm custom slash command regression (#7008)

* point mattermost-redux to webapp-4.0 latest (#7040)

* If login is using mobile respond with JSON object (#7030)

* Allow regions to be set and honored for S3 driver. (#7010) (#7073)

This is necessary for certain users where
GetBucketLocation API is disabled using IAM
policies. There is a field AmazonS3Region
which we need to re-purpose and use to support
this properly.

Fixes https://github.com/mattermost/platform/issues/6999

* [PLT-7231/PLT-7306] Fix GitLab SSO failure with non-English locale and make config locales more forgiving (#7106)

* make config locales more forgiving by assigning default values

* fix error text

* update per comment

* Minor updates to team

* Another team update

i18n/en.json

@@ -6541,7 +6541,7 @@
   },
   {
     "id": "utils.config.supported_server_locale.app_error",
-    "translation": "Unable to load mattermost configuration file:  DefaultServerLocale must be one of the supported locales"
+    "translation": "Unable to load mattermost configuration file:  DefaultServerLocale must be one of the supported locales. Setting DefaultServerLocale to en as default value."
   },
   {
     "id": "utils.config.validate_locale.app_error",