Commits `263c2aaf` and `35052567` added new annotations and labels to the
openshift-ingress namespace, which is managed by the ingress-operator.

This commit adds logic to reconcile the openshift-ingress namespace
resource during cluster upgrades. To prevent overwriting changes made to
the namespace resource by other controllers (or cluster-admins), the
namespace reconciliation logic added in this commit explicitly syncs
namespace labels and annotations that the operator sets.

pkg/operator/controller/ingress/namespace.go:

Refactor `ensureRouterNamespace` so that it handles creating and updating
the openshift-ingress namespace resource (and nothing else).

Add new functions: `currentRouterNamespace`, `updateRouterNamespace`, &
`routerNamespaceChanged`.

Move existing Service Account and Cluster Role Binding creation logic
into new functions, `ensureRouterServiceAccount`, and
`ensureRouterClusterRoleBinding`.

pkg/operator/controller/ingress/controller.go:

Update `ensureRouterNamespace` calling site. Add new calling sites
for `ensureRouterServiceAccount` and `ensureRouterClusterRoleBinding`.

This commit resolves Bug 1954330.