[MM-63513] Turn Cross team search feature flag into a setting option (#30518)

* feat: Add EnableCrossTeamSearch configuration option to ServiceSettings

* feat: Add EnableCrossTeamSearch configuration option to ServiceSettings

* feat: Enable cross-team search by default

* include old FF in client config

server/config/client.go

@@ -101,6 +101,10 @@ func GenerateClientConfig(c *model.Config, telemetryID string, license *model.Li
 	props["DisableWakeUpReconnectHandler"] = strconv.FormatBool(*c.ExperimentalSettings.DisableWakeUpReconnectHandler)
 	props["UsersStatusAndProfileFetchingPollIntervalMilliseconds"] = strconv.FormatInt(*c.ExperimentalSettings.UsersStatusAndProfileFetchingPollIntervalMilliseconds, 10)
 
+	// Here we set the new option, but we also send the old FeatureFlag property for backwards compatibility on mobile < 2.27
+	props["EnableCrossTeamSearch"] = strconv.FormatBool(*c.ServiceSettings.EnableCrossTeamSearch)
+	props["FeatureFlagExperimentalCrossTeamSearch"] = strconv.FormatBool(*c.ServiceSettings.EnableCrossTeamSearch)
+
 	// Set default values for all options that require a license.
 	props["ExperimentalEnableAuthenticationTransfer"] = "true"
 	props["LdapNicknameAttributeSet"] = "false"