[improvement](fe) Make max_user_connections upper bound follow qe_max_connection

[HonestManXin]

Previously the per-user connection limit max_user_connections was hard-coded to a maximum of 10000. When operators raised the FE global connection limit qe_max_connection above 10000, a single user could not be granted more than 10000 connections, which is unreasonable since the effective limit is already bounded by the global setting.

Now the upper bound of max_user_connections is Math.max(qe_max_connection,10000), so a user can be configured up to the global limit while still keeping the original 10000 floor for backward compatibility.

[hello-stephen]

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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.
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[HonestManXin]

/review

[github-actions]

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[HonestManXin]

run buildall

[hello-stephen]

FE UT Coverage Report

Increment line coverage 33.33% (1/3) 🎉
Increment coverage report
Complete coverage report

[hello-stephen]

FE Regression Coverage Report

Increment line coverage 2.04% (1/49) 🎉
Increment coverage report
Complete coverage report