pkg/lightning: retry individual scatter region (#46245)

[ti-chi-bot]

This is an automated cherry-pick of #46245

What problem does this PR solve?

Issue Number: ref #46203

Problem Summary:
Lightning try to scatter all the regions and at the end it backoff and retry it again. It causes few issues

1. If we are hiting a store limit, than further scatter regions cause unnecessarily load on PD.
2. Regions can be skewed as stores are allocated based on number of scatter operation scheduled. It doesn't take into number of scatter operations cancelled because of store limit.

What is changed and how it works?

I am proposing the change similar to tikv go client which doesn't retry and back off after scattering all the regions.

https://github.com/tikv/client-go/blob/a0ac170698524cbf20a869cb3471e969608d599a/tikv/split_region.go#L198

Check List

Tests

• Manual test (add detailed scripts or steps below)

I tested the similar logic in 6.5 and 6.6 by using the below steps

1. Set store limit to 16
2. Parallel import and verify that regions are not skewed

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[ti-chi-bot]

This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

To merge this cherry pick, it must first be approved by the collaborators.

AFTER it has been approved by collaborators, please ping the release team in a comment to request a cherry pick review.

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/test-infra repository.

[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 c4pt0r for approval. For more information see the Kubernetes Code Review Process.

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

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

[D3Hunter]

/hold

[D3Hunter]

closed due to #46203 (comment)