[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/einterfaces/metrics.go

@@ -108,16 +108,16 @@ type MetricsInterface interface {
 	ObserveClientTimeToLastByte(platform, agent, userID string, elapsed float64)
 	ObserveClientTimeToDomInteractive(platform, agent, userID string, elapsed float64)
 	ObserveClientSplashScreenEnd(platform, agent, pageType, userID string, elapsed float64)
-	ObserveClientFirstContentfulPaint(platform, agent string, elapsed float64)
-	ObserveClientLargestContentfulPaint(platform, agent, region string, elapsed float64)
-	ObserveClientInteractionToNextPaint(platform, agent, interaction string, elapsed float64)
-	ObserveClientCumulativeLayoutShift(platform, agent string, elapsed float64)
-	IncrementClientLongTasks(platform, agent string, inc float64)
+	ObserveClientFirstContentfulPaint(platform, agent, userID string, elapsed float64)
+	ObserveClientLargestContentfulPaint(platform, agent, region, userID string, elapsed float64)
+	ObserveClientInteractionToNextPaint(platform, agent, interaction, userID string, elapsed float64)
+	ObserveClientCumulativeLayoutShift(platform, agent, userID string, elapsed float64)
+	IncrementClientLongTasks(platform, agent, userID string, inc float64)
 	ObserveClientPageLoadDuration(platform, agent, userID string, elapsed float64)
-	ObserveClientChannelSwitchDuration(platform, agent, fresh string, elapsed float64)
-	ObserveClientTeamSwitchDuration(platform, agent, fresh string, elapsed float64)
-	ObserveClientRHSLoadDuration(platform, agent string, elapsed float64)
-	ObserveGlobalThreadsLoadDuration(platform, agent string, elapsed float64)
+	ObserveClientChannelSwitchDuration(platform, agent, fresh, userID string, elapsed float64)
+	ObserveClientTeamSwitchDuration(platform, agent, fresh, userID string, elapsed float64)
+	ObserveClientRHSLoadDuration(platform, agent, userID string, elapsed float64)
+	ObserveGlobalThreadsLoadDuration(platform, agent, userID string, elapsed float64)
 	ObserveMobileClientLoadDuration(platform string, elapsed float64)
 	ObserveMobileClientChannelSwitchDuration(platform string, elapsed float64)
 	ObserveMobileClientTeamSwitchDuration(platform string, elapsed float64)