feat: add stage level metrics for update run

[britaniar]

Description of your changes

Fixes #

I have:

• Added two stage level histogram metrics:

  1. One to see how long a user takes to approve the before/after stage approval requests
  2. How long it takes a stage to complete excluding all stage tasks.

• Added an integration case for testing only before stage task (missed previously and added to test the new metric)

• Updated integrations tests to validate new emitted metrics.

• Run make reviewable to ensure this PR is ready for review.

How has this code been tested

• Integration Test

Special notes for your reviewer

What the metrics look like:

fleet_workload_update_run_stage_cluster_updating_duration_seconds_bucket{namespace="prod",name="run-42",le="10"} 1
fleet_workload_update_run_stage_cluster_updating_duration_seconds_bucket{...,le="30"} 4
fleet_workload_update_run_stage_cluster_updating_duration_seconds_bucket{...,le="60"} 7
...
fleet_workload_update_run_stage_cluster_updating_duration_seconds_bucket{...,le="+Inf"} 9

fleet_workload_update_run_stage_cluster_updating_duration_seconds_sum{...} 1450
fleet_workload_update_run_stage_cluster_updating_duration_seconds_count{...} 9

fleet_workload_update_run_approval_request_latency_seconds_bucket{namespace="prod",name="run-42",stageTask="approve",le="60"} 3
fleet_workload_update_run_approval_request_latency_seconds_bucket{...,le="300"} 8
fleet_workload_update_run_approval_request_latency_seconds_bucket{...,le="900"} 12
...
fleet_workload_update_run_approval_request_latency_seconds_bucket{...,le="+Inf"} 15

fleet_workload_update_run_approval_request_latency_seconds_sum{...} 12450
fleet_workload_update_run_approval_request_latency_seconds_count{...} 15

[codecov]

Codecov Report

❌ Patch coverage is 91.83673% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pkg/controllers/updaterun/metrics.go	90.24%	2 Missing and 2 partials ⚠️

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