[skip ci]Add Code Review Rules for Milvus (#7825)

Signed-off-by: xiaofan-luan <xiaofan.luan@zilliz.com>

CODE_REVIEW.md

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+# Milvus Code Review Guide
+
+All PRs are checked in automatically by the sre-robot, with the following condition:
+
+1. DCO check passed
+2. All test passed and code coverage check passed, with a "ci-passed" label
+4. Reviewe passed, with a "lgtm" label
+5. Approver passed, with a "approved" label
+
+Generally speaking, reviewer is volunteered and can be anyone in the community who is familiar with the packages the PR modifies. Reviewers are responsible for the logic correctness, error handling, unit test coverage and code readability. While Approver focus on overall design, code readability, and ensuring the PR follows code of conduct(Such as meaningful title and commit message, marked with correct labels, meaningful comments). Currently, all Approvers are listed under OWNERS_ALIASES file.
+
+
+## Things to do before review
+
+* Read the title, commit message and related issue of the PR, if it's not easy to understand, ask for improvement
+
+* For a bug fix PR, there should be a detailed bug description in related issue, and make sure there test cases to cover this bug.
+
+* For a function enhancement PR, understand the function use case, make sure the functionality is reasonable.
+
+* For a performance PR, make sure benchmark result is listed in PR.
+
+* Think deeply about why is the solution necessary, any workaround or substitutions?
+
+
+## Things to check during the review
+
+* Does the code follow style guide?
+
+* Does the code do excatly the same as title and commit message describe?
+
+* Can this function and variable's behavior be inferred by its name
+
+* Do unit tests cover all the important code branches?
+
+* What about the edge cases and failure handling path?
+
+* Do we need better layering and abstraction? 
+
+* Are there enough comments to understand the intent of the code?
+
+* Are hacks, workarounds and temporary fixes commented?
+
+
+## Things to keep in mind when you are writing a review comment
+
+* Be kind to the coder, not to the code.
+
+* Ask questions rather than make statements.
+
+* Treat people who know less than you with respect, deference, and patience.
+
+* Remember to praise when the code quality exceeds your expectation.
+
+* It isn't necessarily wrong if the coder's solution is different than yours.
+
+* Community is not only about the product, it is about person. Help others to improve whenever possible.
+
+## For Approvers 
+
+Besides All the reviewer's responsibility listed above, Approvers should also maintain code of conduct.
+
+* Be sure the pr has only one commit, author has to do a squash commit in local REPO
+
+* Commit message starts with a capital letter and does not end with punctuation
+
+* Commit message is clear and meaningful. You can only have title but no body if the title is self explained
+
+* PR links to the correct issue, which clearly states the problems to be solved and the planned solution
+
+* PR sets kind label
+
+* The variable names appearing in the source code need to be readable. Comments are necessary if it is a unusual abbreviations
+
+Thanks for [Code Review guide](https://github.com/pingcap/tidb/blob/master/code_review_guide.md) from Pingcap commutity.