[dev](code-owner) add code owner for optimizer and mtmv

[morrySnow]

What problem does this PR solve?

Issue Number: close #xxx

Related PR: #xxx

Problem Summary:

Release note

None

Check List (For Author)

• Test

  • Regression test
  • Unit Test
  • Manual test (add detailed scripts or steps below)
  • No need to test or manual test. Explain why:
    • This is a refactor/code format and no logic has been changed.
    • Previous test can cover this change.
    • No code files have been changed.
    • Other reason

• Behavior changed:

  • No.
  • Yes.

• Does this need documentation?

  • No.
  • Yes.

Check List (For Reviewer who merge this PR)

• Confirm the release note
• Confirm test cases
• Confirm document
• Add branch pick label

[hello-stephen]

Thank you for your contribution to Apache Doris.
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Please clearly describe your PR:

1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
2. Which behaviors were modified. What was the previous behavior, what is it now, why was it modified, and what possible impacts might there be.
3. What features were added. Why was this function added?
4. Which code was refactored and why was this part of the code refactored?
5. Which functions were optimized and what is the difference before and after the optimization?

[morrySnow]

run buildall

[morrySnow]

/review

[github-actions]

I found one completeness issue in the CODEOWNERS update. The new rules cover optimizer/MTMV main sources, but the matching FE unit-test packages are still uncovered, so test-only changes in these areas will not request the same owners.

Critical checkpoint conclusions:

• Goal/test: The goal is to add CODEOWNERS for optimizer and MTMV. It is partially achieved for main sources and parser grammar, but not for existing FE unit-test packages. No runtime tests are needed for CODEOWNERS-only metadata.
• Scope: The change is small and focused, but incomplete for the stated ownership scope.
• Concurrency/lifecycle/config/compatibility/data correctness/transactions/observability: Not applicable; this is repository metadata only.
• Parallel paths: Main source paths were updated, but corresponding test paths were not.
• Test coverage: Not applicable to runtime behavior; local diff whitespace check passed.

User focus: No additional user-provided review focus was specified.

[github-actions]

These new rules cover the main MTMV and Nereids source packages, but the corresponding FE unit-test packages are still uncovered: fe/fe-core/src/test/java/org/apache/doris/mtmv and fe/fe-core/src/test/java/org/apache/doris/nereids. This means a PR that only changes optimizer/MTMV tests will not request these owners, which makes the CODEOWNERS coverage incomplete for the same components. Please add matching test-directory entries near the existing fe/fe-core/src/test/java/... block.

[github-actions]

PR approved by at least one committer and no changes requested.

test is ok