*: merge BR into TiDB

[3pointer]

What problem does this PR solve?

Issue Number: close #26880

Problem Summary: Merge BR repo into TiDB. and resolve the cycle dependence in BR and TiDB.

What is changed and how it works?

Don't review this PR. because it has the whole br repo files change.
Review 3pointer#2 instead.

This PR is used to trigger CI.

Check List

Tests

• Unit test
• Integration test

Release note

Merge BR repo into TiDB to resolve the cycle dependence between these two repos.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• YuJuncen
• bb7133
• wjhuang2016

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[3pointer]

/run-all-tests

[tisonkun]

@3pointer may we create an issue to describe the step? I think it is nit to have a proposal but an issue it necessary.

[tisonkun]

I'd regard forum post as a pre discussion to gather suggestion.

[3pointer]

/run-unit-tests

[3pointer]

/run-integration-tests

[tisonkun]

@3pointer is it true that we don't need a release note for this change? I think it changes BR import path at least.

[YuJuncen]

LGTM, and some hints for the following reviewers:

1. Among the ~200 files, most of them are trivial import path fix, don't panic.
2. The non-trivial changes are mainly clustered at project config files, say, Makefile, log.go, etc..

[3pointer]

/run-check_dev_2

[3pointer]

/run-check_dev_2

[tisonkun]

@wjhuang2016 @YuJuncen if this PR is good to go, would you mind to help on merging?

[bb7133]

IMHO there are several next step TODOs:

• Add missing licenses like br/pkg/backup/client_test.go(with only partial license info) and br/pkg/gluetikv/glue_test.go(no license info).
• Fix the wrong link path for some docs like the br/web/README.md: https://github.com/pingcap/tidb/pull/26655/files#diff-a4215b014bacea6c95f174f4d5e80665b780d035062f793dab6ab0a6c3a33309R75
• Have a discussion on the move of br/docs/br/docs/cn to docs/design//docs/design/cn maybe.

But they are not related to code engineering itself, we do not have to finish it in this PR.

[bb7133]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 049a8e1

[ti-chi-bot]

@3pointer: Your PR was out of date, I have automatically updated it for you.

At the same time I will also trigger all tests for you:

/run-all-tests

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