Fix compact backup labels and sharded compact options

[RidRisR]

What changed

• Add compact-backup-specific label keys and label builder helpers.
• Use CompactBackup instance labels when creating compact Jobs and Pods.
• Stop labeling compact Jobs with backup-specific labels.
• Align compact backup label values with the regional CR naming by using compactbackup.
• Add physicalFileCacheCapacity and name fields to CompactSpec for sharded compact configuration.
• Pass configured physicalFileCacheCapacity to tikv-ctl as --physical-file-cache-capacity instead of using the hard-coded value.
• Default omitted or empty physicalFileCacheCapacity to 0 in backup-manager options.
• Validate provided physicalFileCacheCapacity values as Kubernetes quantities and reject negative values while allowing 0.
• Pass configured name to tikv-ctl as --name only when it is set.
• Keep passing --crr-checkpoint-prefix crr-checkpoint for every sharded compact job, including when --until is set explicitly.
• Stop passing --replication-status-sub-prefix=crr-checkpoint to BR for replication restore; newer BR resolves the checkpoint state itself.
• Update CRDs, OpenAPI, API reference docs, and regression tests.

Why

CompactBackup Jobs used a hard-coded app.kubernetes.io/instance value and backup-specific labels. Anti-affinity selectors that target the actual CompactBackup or BackupSchedule instance could not match compact Pods, allowing multiple compact Pods to schedule onto the same node.

Sharded compact also needs user-facing YAML configuration for tikv-ctl --physical-file-cache-capacity and --name. physicalFileCacheCapacity now has a friendlier default: users may omit it and backup-manager will pass 0, while invalid or negative explicit values are still rejected.

For replication restore, newer BR can parse crr-checkpoint/resume-state.json directly, so the operator no longer needs to pass the replication status sub-prefix. Sharded compact still needs the checkpoint prefix for tikv-ctl to locate the replication checkpoint state, even when an explicit EndTs produces --until.

Validation

• GOCACHE=/tmp/tidb-operator-go-build go test ./pkg/controller/compactbackup ./cmd/backup-manager/app/compact/options -count=1
• go test ./cmd/backup-manager/app/restore ./cmd/backup-manager/app/compact ./pkg/backup/restore
• rg -n "physicalFileCacheCapacity.*required when mode is sharded|required when mode is sharded" docs/api-references/docs.md pkg/apis/pingcap/v1alpha1 cmd/backup-manager/app/compact pkg/controller/compactbackup -S
• git diff --check a650aa3ce1e66bb28d76e75fd88d6daef569ec91...HEAD

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@RidRisR: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-e2e-kind-scale-simultaneously	46ebe7e	link	false	/test pull-e2e-kind-scale-simultaneously
pull-e2e-kind-basic	46ebe7e	link	false	/test pull-e2e-kind-basic
pull-e2e-kind-dmcluster	46ebe7e	link	false	/test pull-e2e-kind-dmcluster
pull-e2e-kind-tngm	46ebe7e	link	false	/test pull-e2e-kind-tngm
pull-e2e-kind-serial	46ebe7e	link	false	/test pull-e2e-kind-serial

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