[fix](remote scan) Fix remote scan paralism

[zhiqiang-hhhh]

Introduced by #41273.

The modification of _max_scan_thread_num is a long story. So, the modification i will describe only contains three timestamp. 1. Before #41273; 2. After #41273; 3. After this pr.

We have two dimension, so i will use a table. The value of the table is the _max_scan_thread_num when queries running serially.

C refers to num of cpu cores.

1. Before 41273

Engine	OLAPScanOperator	FileScanOperator
PipelineX	min(2C, num_of_scanner)	4
Old-Pipeline	4	4
Non-Pipeline	4	4

2. After 41273

Engine	OLAPScanOperator	FileScanOperator
PipelineX	min(2C, num_of_scanner)	min(2C, num_of_scanner)
Old-Pipeline	4	4
Non-Pipeline	4	4

3. After this pr

Engine	OLAPScanOperator	FileScanOperator
PipelineX	min(2C, num_of_scanner)	4
Old-Pipeline	4	4
Non-Pipeline	4	4

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[zhiqiang-hhhh]

run buildall

[zhiqiang-hhhh]

run buildall

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[zhiqiang-hhhh]

run buildall

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[zhiqiang-hhhh]

run buildall

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[doris-robot]

TeamCity be ut coverage result:
Function Coverage: 36.02% (9368/26005)
Line Coverage: 27.58% (76953/278969)
Region Coverage: 26.37% (39531/149907)
Branch Coverage: 23.15% (20108/86844)
Coverage Report: http://coverage.selectdb-in.cc/coverage/f4d462968f2375c3b54d83e0a72c9065d9ed4f55_f4d462968f2375c3b54d83e0a72c9065d9ed4f55/report/index.html

[yiguolei]

should set default value