Remove deprecated OnePerHost pod-distribution value #1978

The OnePerHost pod-distribution value is dead code: the constant is marked // Deprecated value at pkg/apis/deployment/affinity.go:55, and no switch in pkg/model/common/affinity/pod-anti-affinity.go or pkg/model/common/normalizer/templates/pod.go matches it. A user-supplied OnePerHost is silently normalized to Unspecified and produces no affinity rules — i.e. it looks like it works but does nothing.

It should be cleaned out of:

1. Go constant — pkg/apis/deployment/affinity.go:55 (PodDistributionOnePerHost = "OnePerHost").
2. CRDs — drop "OnePerHost" from the distribution/podDistribution.type enum in:
   • deploy/operatorhub/<current-version>/clickhouseinstallations.clickhouse.altinity.com.crd.yaml
   • deploy/operatorhub/<current-version>/clickhouseinstallationtemplates.clickhouse.altinity.com.crd.yaml
   • deploy/operatorhub/<current-version>/clickhousekeeperinstallations.clickhouse-keeper.altinity.com.crd.yaml
   • any matching CRDs under deploy/builder/, deploy/helm/, deploy/operator/ that the build pipeline regenerates.
     (Older deploy/operatorhub/0.x.y/ directories are historical snapshots — leave those alone.)
3. Docs — docs/custom_resource_explained.md lines 564–606 still list OnePerHost as a valid distribution value and show it in two examples. Replace with the supported equivalents (type: ClickHouseAntiAffinity or type: MaxNumberPerNode, number: 1).
4. Examples — docs/chit-examples/104-templates.yaml uses a top-level distribution: "OnePerHost" field that doesn't even exist on PodTemplate in the Go types. Rewrite using podDistribution:.
5. Requirements — mention in tests/requirements/requirements.md:1016.

Compatibility note

Removing the enum value is technically a breaking CRD change for any user who literally wrote OnePerHost. Since the value already does nothing, the user impact is just a validation error instead of silent no-op — arguably an improvement, but worth calling out in the release notes.