Fix Video Unavailable problem at YouTube preview (#26980)

* Fix YouTube preview shows Video Unavailable

* Fix typo on iframe property

* Remove duplicated property

* fix lint error (double-quotes, unknown property)

* renew snapshot for youtube_video.tsx

* fix double quotes and newline error on snapshot for youtube_video.tsx

* fix blank on snapshot for youtube_video.tsx

* Add YouTube Shorts Embed Preview

* Revert "Add YouTube Shorts Embed Preview"

This reverts commit b5fb7a4076ef73774a0e50157f371516b9d383b2.

* Add setting for Youtube Referrer Policy

* fix test code error about Youtube Referrer Policy

* remove mistake changes on `webpack.config.js`

* add test and snapshot about `youtubeReferrerPolicy = true`

* fix errors on ci

* update description of YouTube Referrer Policy

* remove unnecessary whitespace in default_config.ts

* remove ko.json changes to prevent conflict with translate tool

* update snapshot of `youtube_video.test.tsx`

* referrerPolicy on `youtube_video` didn't follow global policy value

https://github.com/mattermost/mattermost/pull/26980#discussion_r1672524152

* update snapshot of `youtube_video.test.tsx`

* Remove obsolete snapshot

* fix typo on index.ts @ youtube_video

---------

Co-authored-by: Mattermost Build <build@mattermost.com>
Co-authored-by: Harrison Healey <harrisonmhealey@gmail.com>

server/public/model/config.go

@@ -1075,6 +1075,7 @@ type ExperimentalSettings struct {
 	DelayChannelAutocomplete                              *bool   `access:"experimental_features"`
 	DisableWakeUpReconnectHandler                         *bool   `access:"experimental_features"`
 	UsersStatusAndProfileFetchingPollIntervalMilliseconds *int64  `access:"experimental_features"`
+	YoutubeReferrerPolicy                                 *bool   `access:"experimental_features"`
 }
 
 func (s *ExperimentalSettings) SetDefaults() {
@@ -1121,6 +1122,10 @@ func (s *ExperimentalSettings) SetDefaults() {
 	if s.UsersStatusAndProfileFetchingPollIntervalMilliseconds == nil {
 		s.UsersStatusAndProfileFetchingPollIntervalMilliseconds = NewPointer(int64(ExperimentalSettingsDefaultUsersStatusAndProfileFetchingPollIntervalMilliseconds))
 	}
+
+	if s.YoutubeReferrerPolicy == nil {
+		s.YoutubeReferrerPolicy = NewBool(false)
+	}
 }
 
 type AnalyticsSettings struct {