ddl: support ALTER PLACEMENT POLICY ...

[lcwangchao]

What problem does this PR solve?

Issue Number: close #27714

Check List

Tests

• Unit test

Release note

ddl: support `ALTER PLACEMENT POLICY ...`

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• AilinKid
• xhebox

To complete the pull request process, please ask the reviewers in the list to review by filling /cc @reviewer in the comment.
After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

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

Reviewer can indicate their review by submitting an approval review.
Reviewer can cancel approval by submitting a request changes review.

[morgo]

LGTM, but I don't know ddl well. I will leave for others to approve.

[AilinKid]

Rest LGTM

[AilinKid]

/merge

[ti-chi-bot]

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

Commit hash: 5ec9072

[lcwangchao]

/run-check_dev_2

[AilinKid]

/run-check_dev_2

[2021-09-03T09:16:22.657Z] placement_policy_test.go:222:

[2021-09-03T09:16:22.657Z] c.Assert(err.Error(), Equals, ca.errmsg)

[2021-09-03T09:16:22.657Z] ... obtained string = "" +

[2021-09-03T09:16:22.657Z] ... "invalid label constraints format: should be [constraint1, ...] (error yaml: unmarshal errors:\n" +

[2021-09-03T09:16:22.657Z] ... " line 1: cannot unmarshal !!map into []string)"

[2021-09-03T09:16:22.657Z] ... expected string = "" +

[2021-09-03T09:16:22.657Z] ... "[ddl:-1]invalid label constraints format: should be [constraint1, ...] (error yaml: unmarshal errors:\n"

[2021-09-03T09:16:22.657Z] ... " line 1: cannot unmarshal !!map into []string)"

[ti-chi-bot]

@lcwangchao: Your PR was out of date, I have automatically updated it for you.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

If the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

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 ti-community-infra/tichi repository.

[AilinKid]

/merge

[ti-chi-bot]

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

Commit hash: a7b185a