[ws-manager] add metrics to track initialize and finalize of workspaces

[sagor999]

Description

Add metrics to track initialize (time it takes to download and untar backup for example or to load prebuild) and finalize (time it takes to create and upload backup of workspace).
This metrics will be used later on to compare them to PVC implementation.

Related Issue(s)

Fixes #9353

How to test

Spin up new workspace preview environment using installer from this PR
Create new workspace, create large file in workspace and stop workspace.
Then open that workspace again.
Port forward metrics port of ws-manager and look for new metrics.
Times reported will match the time it took to finalize or initialize the workspace.

Release Notes

[ws-manager] add metrics to track initialize and finalize of workspaces

Documentation

[jenting]

Would it be better that calculate the start time at finalizeWorkspaceContent and have a defer function to calculate the end time? For example:

func (m *Monitor) finalizeWorkspaceContent(ctx context.Context, wso *workspaceObjects) {
    t := time.Now()
    ...
    tpe, err := wso.WorkspaceType()
    if err != nil {
        tracing.LogError(span, err)
        log.WithError(err).Warn("cannot determine workspace type - assuming this is a regular")
        tpe = api.WorkspaceType_REGULAR
    }
    defer func() {
        wsType := api.WorkspaceType_name[int32(tpe)]
	hist, errHist := m.manager.metrics.finalizeTimeHistVec.GetMetricWithLabelValues(wsType)
	if errHist != nil {
		log.WithError(errHist).WithField("type", wsType).Warn("cannot get finalize time histogram metric")
	}
	hist.Observe(time.Since(t).Seconds())
    }()
    ...
}

[sagor999]

Yeah, I thought of that, but that would catch incorrect metrics in case of this return statement:

gitpod/components/ws-manager/pkg/manager/monitor.go

Lines 929 to 933 in 054bd0b

	if !didSometing {
	// someone else is managing finalization process ... we don't have to bother
	return
	}

I only want to catch timing for workspaces where we actually did some work.