[fix](web) FE startup fail due to websocket startup

[gavinchou]

Summary

Pick #60369 to branch-4.1

Changes

• Fix FE startup failure when enable_https=true by using Spring Boot's addServerCustomizers() hook to initialize WebSocket support before WebAppContext starts
• Compatible with branch-4.1's existing HTTP header size configuration

Test

• FE build passed

Related Issue

close #60366

[hello-stephen]

Thank you for your contribution to Apache Doris.
Don't know what should be done next? See How to process your PR.

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?

[gavinchou]

run buildall

[gavinchou]

run buildall

[hello-stephen]

FE Regression Coverage Report

Increment line coverage 30.00% (6/20) 🎉
Increment coverage report
Complete coverage report

[yiguolei]

skip buildall

[github-actions]

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

[github-actions]

PR approved by anyone and no changes requested.