[Enhancement] Support to specify warehouse for sr flink source connector

[zhangbutao]

What type of PR is this：

• BugFix
• Feature
• Enhancement
• Refactor
• UT
• Doc
• Tool

Which issues of this PR fixes ：

This PR is used for StarRocks/starrocks#57930
Support to specify warehouse for sr flink source connector using param `'scan.params.warehouse'='warehosue_name', and then pass the warehouse to fe through http header.

CREATE TABLE flink_test
(
    `id` INT,
    `name` STRING,
    `score` INT
)
WITH
(
    'connector'='starrocks',
    'scan-url'='192.168.xxx.xxx:8030',
    'jdbc-url'='jdbc:mysql://192.168.xxx.xxx:9030',
    'username'='xxxxxx',
    'password'='xxxxxx',
    'database-name'='test',
    'table-name'='score_board',
    'scan.params.warehouse'='warehosue_name'
);

`
Fixes #

Problem Summary(Required) ：

Checklist:

• I have added test cases for my bug fix or my new feature
• This pr will affect users' behaviors
• This pr needs user documentation (for new or modified features or behaviors)
• I have added documentation for my new feature or new function

[kevincai]

what's the default value if the specific key is not configured?

[zhangbutao]

@kevincai I refine this code to avoid setting warehouse header(null value) in case of flink sink table not having 'scan.params.warehouse'='warehosue_name'. And then fe will use the default_warehouse if not getting the warehouse header.

[zhangbutao]

Can we merge this change? @kevincai
Thanks.