Add comments outlining the worries against using FirebaseSessionsEnabled (#10784)

Author: samedson

FirebaseSessions/README.md

@@ -34,7 +34,9 @@ You can access command line parameters by following: Press `CMD-Shift-,` => Run
 #### Overriding Settings
 You can override the Settings values fetched from the server using the app's Info.plist. The full list of override plist keys can be found in `LocalOverrideSettings.swift`.
 
- - **FirebaseSessionsEnabled**: Bool representing whether to make any network calls
+ - **FirebaseSessionsEnabled**: Bool representing whether to send Session Events (does not affect Settings requests). We would recommend apps against using this to disable data collection, and instead disable it via products' public data collection APIs.
+     - If any apps use this flag to disable the Firebase Sessions SDK, keep in mind this may break future metrics features with products like FirePerf and Crashlytics.
+     - This flag is internal and may break in a future version of FirebaseSessions
  - **FirebaseSessionsTimeout**: Float number of seconds representing the time that an app must be backgrounded before generating a new session
  - **FirebaseSessionsSampingRate**: Float between 0 and 1 representing how often events are sent. 0 is drop everything, 1 is send everything.
 

FirebaseSessions/Sources/Settings/LocalOverrideSettings.swift

@@ -17,6 +17,13 @@ import Foundation
 
 /// Class that manages the local overrides configs related to the library.
 class LocalOverrideSettings: SettingsProvider {
+  // This will disable Sessions SDK Events, but not Settings requests.
+  // If any apps use this flag to disable the Firebase Sessions SDK,
+  // keep in mind this may break metrics future features with products like
+  // FirePerf and Crashlytics. As a result, we would recommend apps
+  // use another way to disable data collection (like disabling it via
+  // the product public data collection APIs themselves).
+  // This flag is internal and may break in the future.
   static let PlistKey_sessions_enabled = "FirebaseSessionsEnabled"
   static let PlistKey_sessions_timeout = "FirebaseSessionsTimeout"
   static let PlistKey_sessions_samplingRate = "FirebaseSessionsSampingRate"