[aider assisted] MM-61888: Add ClientSideUserIds field to MetricsSettings (#30127)

We add a new config setting to allow the admin to set a fixed
list of userIDs to track for all client side webapp metrics.

This gives the admin to get a deeper look at how the application
is behaving for a single user.

A new section in the system console is also added for the user
to edit this setting from the UI.

https://mattermost.atlassian.net/browse/MM-61888

```release-note
A new config setting MetricsSettings.ClientSideUserIds is added
where you can set the user ids you want to track for client side webapp
metrics.
```

* fix lint errors

```release-note
NONE
```

* fixing tests

```release-note
NONE
```

server/public/model/config.go

@@ -1071,11 +1071,12 @@ func (s *ClusterSettings) SetDefaults() {
 }
 
 type MetricsSettings struct {
-	Enable                    *bool   `access:"environment_performance_monitoring,write_restrictable,cloud_restrictable"`
-	BlockProfileRate          *int    `access:"environment_performance_monitoring,write_restrictable,cloud_restrictable"`
-	ListenAddress             *string `access:"environment_performance_monitoring,write_restrictable,cloud_restrictable"` // telemetry: none
-	EnableClientMetrics       *bool   `access:"environment_performance_monitoring,write_restrictable,cloud_restrictable"`
-	EnableNotificationMetrics *bool   `access:"environment_performance_monitoring,write_restrictable,cloud_restrictable"`
+	Enable                    *bool    `access:"environment_performance_monitoring,write_restrictable,cloud_restrictable"`
+	BlockProfileRate          *int     `access:"environment_performance_monitoring,write_restrictable,cloud_restrictable"`
+	ListenAddress             *string  `access:"environment_performance_monitoring,write_restrictable,cloud_restrictable"` // telemetry: none
+	EnableClientMetrics       *bool    `access:"environment_performance_monitoring,write_restrictable,cloud_restrictable"`
+	EnableNotificationMetrics *bool    `access:"environment_performance_monitoring,write_restrictable,cloud_restrictable"`
+	ClientSideUserIds         []string `access:"environment_performance_monitoring,write_restrictable,cloud_restrictable"` // telemetry: none
 }
 
 func (s *MetricsSettings) SetDefaults() {
@@ -1098,6 +1099,23 @@ func (s *MetricsSettings) SetDefaults() {
 	if s.EnableNotificationMetrics == nil {
 		s.EnableNotificationMetrics = NewPointer(true)
 	}
+
+	if s.ClientSideUserIds == nil {
+		s.ClientSideUserIds = []string{}
+	}
+}
+
+func (s *MetricsSettings) isValid() *AppError {
+	const maxLength = 5
+	if len(s.ClientSideUserIds) > maxLength {
+		return NewAppError("MetricsSettings.IsValid", "model.config.is_valid.metrics_client_side_user_ids.app_error", map[string]any{"MaxLength": maxLength, "CurrentLength": len(s.ClientSideUserIds)}, "", http.StatusBadRequest)
+	}
+	for _, id := range s.ClientSideUserIds {
+		if !IsValidId(id) {
+			return NewAppError("MetricsSettings.IsValid", "model.config.is_valid.metrics_client_side_user_id.app_error", map[string]any{"Id": id}, "", http.StatusBadRequest)
+		}
+	}
+	return nil
 }
 
 type ExperimentalSettings struct {
@@ -3806,6 +3824,10 @@ func (o *Config) IsValid() *AppError {
 		return NewAppError("Config.IsValid", "model.config.is_valid.cluster_email_batching.app_error", nil, "", http.StatusBadRequest)
 	}
 
+	if appErr := o.MetricsSettings.isValid(); appErr != nil {
+		return appErr
+	}
+
 	if appErr := o.CacheSettings.isValid(); appErr != nil {
 		return appErr
 	}