ddl: Ensure feature flag support for placement rules

[sylzd]

What problem does this PR solve?

Issue Number: close #29088

Problem Summary:

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

None

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[sylzd]

/cc @morgo @xhebox @AilinKid

[xhebox]

LGTM, but I am thinking about check it in ddl, maybe combine with checkAndNormalize function... It is also strange that we return ddl error in the planner package.

[morgo]

Getting an error from the linter:

[2021-10-29T14:18:44.653Z] planner/core/preprocess_test.go:18: File is not `goimports`-ed (goimports)
[2021-10-29T14:18:44.653Z] 	"context"

I think you will also need to run make errdoc because there is a new error.

[sylzd]

Actually, I started a new pr #29258 and I prefer the new implement 🤣

[sylzd]

Duplicated with #29258