fix log backup state query failure handling

[RidRisR]

What changed

This updates log backup tracker state queries to distinguish critical PD etcd query failures from confirmed missing metadata:

• Treat info key query failures as unknown state instead of task-not-found.
• Start a 10-minute critical query failure countdown for info query failures and PD etcd client creation failures.
• Report BackupFailed / LogBackupStateQueryFailed only once per continuous failure window, and retry reporting if the status update itself fails.
• Treat pause key query failures as partial state: keep usable info/checkpoint data, skip kernel state sync, and avoid marking the backup failed.
• Preserve checkpoint updates when pause state is unknown.

Why

A transient PD/etcd/DNS issue could previously leave InfoExists=false and be interpreted as LogBackupTaskNotFound, incorrectly failing log backup even though task existence was unknown.

Validation

• GOCACHE=/tmp/go-cache go test ./pkg/backup/backup -count=1
• GOCACHE=/tmp/go-cache go test -race ./pkg/backup/backup -count=1

[ti-chi-bot]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please assign sdojjy for approval. For more information see the Code Review Process.
Please ensure that each of them provides their approval before proceeding.

The full list of commands accepted by this bot can be found here.

Details

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[ti-chi-bot]

@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	02407b6	link	false	/test pull-e2e-kind-scale-simultaneously
pull-e2e-kind-tngm	02407b6	link	false	/test pull-e2e-kind-tngm
pull-e2e-kind-dmcluster	02407b6	link	false	/test pull-e2e-kind-dmcluster
pull-e2e-kind-basic	02407b6	link	false	/test pull-e2e-kind-basic
pull-e2e-kind-tidbcluster	02407b6	link	false	/test pull-e2e-kind-tidbcluster
pull-e2e-kind-br	02407b6	link	false	/test pull-e2e-kind-br
pull-e2e-kind-across-kubernetes	02407b6	link	false	/test pull-e2e-kind-across-kubernetes
pull-e2e-kind-serial	02407b6	link	false	/test pull-e2e-kind-serial

Full PR test history. Your PR dashboard.

Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository. I understand the commands that are listed here.