MM-11120 Adding setting to disable email invitations and rate limiting. (#9063)

* Adding setting to disable email invitations.

* Adding a setting and rate limiting for email invite sending.

* Modifying email rate limit to 20/user/hour

* Adding EnableEmailInvitations to client side config and command.

utils/config.go

@@ -573,6 +573,8 @@ func GenerateClientConfig(c *model.Config, diagnosticId string, license *model.L
 
 	props["RunJobs"] = strconv.FormatBool(*c.JobSettings.RunJobs)
 
+	props["EnableEmailInvitations"] = strconv.FormatBool(*c.ServiceSettings.EnableEmailInvitations)
+
 	// Set default values for all options that require a license.
 	props["ExperimentalHideTownSquareinLHS"] = "false"
 	props["ExperimentalTownSquareIsReadOnly"] = "false"