conn(dm): add timeout for Conn (#6055)

[ti-chi-bot]

This is an automated cherry-pick of #6055

Signed-off-by: lance6716 lance6716@gmail.com

What problem does this PR solve?

Issue Number: close #3733

What is changed and how it works?

Conn will block until either a connection is returned or ctx is canceled

we manually add a timeout

Check List

Tests

• Unit test

Questions

Will it cause performance regression or break compatibility?

Do you need to update user documentation, design documentation or monitoring documentation?

Release note

 `None`.

[ti-chi-bot]

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[ti-chi-bot]

@ti-chi-bot: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

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