MM-23935 extend session expiry on user activity (#14275)

* MM-23935  extend session expiry on user activity

- if user types anything before a session expires the session will be extended to now + session length

- ensures new session expiries are not written to DB too frequently

- new session store func for updating session ExpiresAt

- session length defaults for mobile and web/ldap changed from 180 days to 30 days

model/config.go

@@ -283,6 +283,7 @@ type ServiceSettings struct {
 	CorsAllowCredentials                              *bool   `restricted:"true"`
 	CorsDebug                                         *bool   `restricted:"true"`
 	AllowCookiesForSubdomains                         *bool   `restricted:"true"`
+	ExtendSessionLengthWithActivity                   *bool   `restricted:"true"`
 	SessionLengthWebInDays                            *int    `restricted:"true"`
 	SessionLengthMobileInDays                         *int    `restricted:"true"`
 	SessionLengthSSOInDays                            *int    `restricted:"true"`
@@ -521,12 +522,25 @@ func (s *ServiceSettings) SetDefaults(isUpdate bool) {
 		s.EnableTutorial = NewBool(true)
 	}
 
+	// Must be manually enabled for existing installations.
+	if s.ExtendSessionLengthWithActivity == nil {
+		s.ExtendSessionLengthWithActivity = NewBool(!isUpdate)
+	}
+
 	if s.SessionLengthWebInDays == nil {
-		s.SessionLengthWebInDays = NewInt(180)
+		if isUpdate {
+			s.SessionLengthWebInDays = NewInt(180)
+		} else {
+			s.SessionLengthWebInDays = NewInt(30)
+		}
 	}
 
 	if s.SessionLengthMobileInDays == nil {
-		s.SessionLengthMobileInDays = NewInt(180)
+		if isUpdate {
+			s.SessionLengthMobileInDays = NewInt(180)
+		} else {
+			s.SessionLengthMobileInDays = NewInt(30)
+		}
 	}
 
 	if s.SessionLengthSSOInDays == nil {