[MM-51412] - In-product banner to communicate Cloud Free deprecation (#22622)

* [MM-51412] - In-product banner to communicate Cloud Free deprecation

* fix lint

* make improvements

* make improvements

* put banners behind feature flag

* cloud free overage case

* add unit tests

* feedback impl

* fix test

* rename and enable feature flag by default

* fix alert banner mode

* read end date from env var

* disable ff by default

* enter cloud free deprecation date

* remove env var

* fix text

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

model/feature_flags.go

@@ -75,6 +75,8 @@ type FeatureFlags struct {
 
 	OnboardingTourTips bool
 
+	DeprecateCloudFree bool
+
 	AppsSidebarCategory bool
 }
 
@@ -101,6 +103,7 @@ func (f *FeatureFlags) SetDefaults() {
 	f.ReduceOnBoardingTaskList = false
 	f.ThreadsEverywhere = false
 	f.GlobalDrafts = true
+	f.DeprecateCloudFree = false
 	f.WysiwygEditor = false
 	f.OnboardingAutoShowLinkedBoard = false
 	f.OnboardingTourTips = true