[Doc] #15310 update doc, db password cannot be empty for DQ tasks

[cncws]

Purpose of the pull request

fix https://github.com/apache/dolphinscheduler/issues/15310 Update the db settings in docs. A password is not required by DS itself, however it's required by DataQuality tasks. It troubled me several days until I read the source code and guess the problem happened with empty db password.

Brief change log

Add a note to some .md file.

Verify this pull request

No source code is modified.

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