Fixes BackendTLSPolicy Status Update data race

[sunjayBhatia]

DAG cache objects were being written to when StatusUpdater fetched resource to perform update on since status updates held a reference to them.

[sunjayBhatia]

See failure: https://github.com/projectcontour/contour/actions/runs/7875556667/job/21487800526?pr=6184

==================
  WARNING: DATA RACE
  Read at 0x00c000c3b4c8 by goroutine 256:
    github.com/projectcontour/contour/internal/dag.(*KubernetesCache).configMapTriggersRebuild()
        /home/runner/work/contour/contour/internal/dag/cache.go:619 +0x169c
    github.com/projectcontour/contour/internal/dag.(*KubernetesCache).remove()
        /home/runner/work/contour/contour/internal/dag/cache.go:326 +0x16b9
    github.com/projectcontour/contour/internal/dag.(*KubernetesCache).Remove()
        /home/runner/work/contour/contour/internal/dag/cache.go:307 +0xf1
    github.com/projectcontour/contour/internal/contour.(*EventHandler).onUpdate()
        /home/runner/work/contour/contour/internal/contour/handler.go:262 +0xf1b
    github.com/projectcontour/contour/internal/contour.(*EventHandler).Start()
        /home/runner/work/contour/contour/internal/contour/handler.go:168 +0x77d
    sigs.k8s.io/controller-runtime/pkg/manager.(*runnableGroup).reconcile.func1()
        /home/runner/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.17.1/pkg/manager/runnable_group.go:223 +0x1ce
    sigs.k8s.io/controller-runtime/pkg/manager.(*runnableGroup).reconcile.func2()
        /home/runner/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.17.1/pkg/manager/runnable_group.go:226 +0x41

  Previous write at 0x00c000c3b4c8 by goroutine 282:
    reflect.typedmemmove()
        /opt/hostedtoolcache/go/1.21.6/x64/src/runtime/mbarrier.go:193 +0x0
    reflect.Value.Set()
        /opt/hostedtoolcache/go/1.21.6/x64/src/reflect/value.go:2265 +0x184
    sigs.k8s.io/controller-runtime/pkg/cache/internal.(*CacheReader).Get()
        /home/runner/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.17.1/pkg/cache/internal/cache_reader.go:99 +0x706
    sigs.k8s.io/controller-runtime/pkg/cache.(*informerCache).Get()
        /home/runner/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.17.1/pkg/cache/informer_cache.go:88 +0x244
    sigs.k8s.io/controller-runtime/pkg/cache.(*delegatingByGVKCache).Get()
        /home/runner/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.17.1/pkg/cache/delegating_by_gvk_cache.go:44 +0x144
    sigs.k8s.io/controller-runtime/pkg/client.(*client).Get()
        /home/runner/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.17.1/pkg/client/client.go:356 +0x551
    github.com/projectcontour/contour/internal/k8s.(*StatusUpdateHandler).apply.func3()
        /home/runner/work/contour/contour/internal/k8s/status.go:123 +0x145
    k8s.io/client-go/util/retry.OnError.func1()
        /home/runner/go/pkg/mod/k8s.io/client-go@v0.29.1/util/retry/util.go:51 +0x41
    k8s.io/apimachinery/pkg/util/wait.runConditionWithCrashProtection()
        /home/runner/go/pkg/mod/k8s.io/apimachinery@v0.29.1/pkg/util/wait/wait.go:145 +0x53
    k8s.io/apimachinery/pkg/util/wait.ExponentialBackoff()
        /home/runner/go/pkg/mod/k8s.io/apimachinery@v0.29.1/pkg/util/wait/backoff.go:461 +0x5e
    k8s.io/client-go/util/retry.OnError()
        /home/runner/go/pkg/mod/k8s.io/client-go@v0.29.1/util/retry/util.go:50 +0x144
    github.com/projectcontour/contour/internal/k8s.(*StatusUpdateHandler).apply()
        /home/runner/work/contour/contour/internal/k8s/status.go:113 +0x6b7
    github.com/projectcontour/contour/internal/k8s.(*StatusUpdateHandler).Start()
        /home/runner/work/contour/contour/internal/k8s/status.go:162 +0x2fb
    sigs.k8s.io/controller-runtime/pkg/manager.(*runnableGroup).reconcile.func1()
        /home/runner/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.17.1/pkg/manager/runnable_group.go:223 +0x1ce
    sigs.k8s.io/controller-runtime/pkg/manager.(*runnableGroup).reconcile.func2()
        /home/runner/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.17.1/pkg/manager/runnable_group.go:226 +0x41

  Goroutine 256 (running) created at:
    sigs.k8s.io/controller-runtime/pkg/manager.(*runnableGroup).reconcile()
        /home/runner/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.17.1/pkg/manager/runnable_group.go:207 +0x250
    sigs.k8s.io/controller-runtime/pkg/manager.(*runnableGroup).Start.func1.2()
        /home/runner/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.17.1/pkg/manager/runnable_group.go:136 +0x33

  Goroutine 282 (running) created at:
    sigs.k8s.io/controller-runtime/pkg/manager.(*runnableGroup).reconcile()
        /home/runner/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.17.1/pkg/manager/runnable_group.go:207 +0x250
    sigs.k8s.io/controller-runtime/pkg/manager.(*runnableGroup).Start.func1.2()
        /home/runner/go/pkg/mod/sigs.k8s.io/controller-runtime@v0.17.1/pkg/manager/runnable_group.go:136 +0x33

[codecov]

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Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6185   +/-   ##
=======================================
  Coverage        ?   79.51%           
=======================================
  Files           ?      142           
  Lines           ?    16243           
  Branches        ?        0           
=======================================
  Hits            ?    12916           
  Misses          ?     3014           
  Partials        ?      313           

Files	Coverage Δ
internal/dag/gatewayapi_processor.go	93.32% <ø> (ø)
internal/status/backendtlspolicyconditions.go	91.37% <ø> (ø)
internal/status/cache.go	93.22% <100.00%> (ø)