issue: #41816
pr #37983 introduced an issue, if doesn't specified
`defaultRootPassword` in milvus.yaml, then `"Milvus"` will be used as
default password for root user, instead of `Milvus`.
This PR fix the unexpected password for root, and add comment for case
which use large numeric password requires double quotes.
Signed-off-by: Wei Liu <wei.liu@zilliz.com>