Set max_final_threads to number of cores by default

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Changelog category (leave one):

• Performance Improvement

Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):

Setting max_final_threads would be set to number of cores at server startup (by the same algorithm as we use for max_threads). This improves concurrency of final execution on servers with high number of CPUs.

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So the new behaviour is: max_final_threads != 0 => value left untouched, otherwise max_threads = cpus. additionally if max_final_threads > max_threads => max_threads streams will be used for reading.

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Stateless tests (debug) [2/5] -

1103067:2023.03.22 22:50:41.732038 [ 15905 ] {5f8a4909-021c-4dca-8898-62add982d015} <Debug> executeQuery: (from [::1]:44762) (comment: 02232_dist_insert_send_logs_level_hung.sh) insert into function remote('127.2', currentDatabase(), in_02232) select * from numbers(1e6) (stage: Complete)
1103068:2023.03.22 22:50:41.734624 [ 15905 ] {5f8a4909-021c-4dca-8898-62add982d015} <Trace> ContextAccess (default): Access granted: CREATE TEMPORARY TABLE, REMOTE ON *.*
1103069:2023.03.22 22:50:41.735063 [ 15905 ] {5f8a4909-021c-4dca-8898-62add982d015} <Trace> Connection (127.2:9000): Connecting. Database: (not specified). User: default
1103076:2023.03.22 22:50:41.978349 [ 15905 ] {5f8a4909-021c-4dca-8898-62add982d015} <Trace> Connection (127.2:9000): Connected to ClickHouse server version 23.3.1.
1103100:2023.03.22 22:50:41.982639 [ 24529 ] {5a964b7a-e48a-4b5c-aba7-479855b3f3db} <Debug> executeQuery: (from [::ffff:127.0.0.1]:48458, initial_query_id: 5f8a4909-021c-4dca-8898-62add982d015) (comment: 02232_dist_insert_send_logs_level_hung.sh) DESC TABLE test_lng7d3ph.in_02232 (stage: Complete)
1103108:2023.03.22 22:50:41.992996 [ 15905 ] {5f8a4909-021c-4dca-8898-62add982d015} <Trace> InterpreterSelectQuery: FetchColumns -> Complete
1103110:2023.03.22 22:50:42.000737 [ 24529 ] {093691bb-350a-4bf9-9e00-e374fd24b86a} <Debug> executeQuery: (from [::ffff:127.0.0.1]:48458, initial_query_id: 5f8a4909-021c-4dca-8898-62add982d015) (comment: 02232_dist_insert_send_logs_level_hung.sh) INSERT INTO test_lng7d3ph.in_02232 (key) VALUES (stage: Complete)
1193749:2023.03.22 22:54:50.477081 [ 15905 ] {5f8a4909-021c-4dca-8898-62add982d015} <Information> TCPHandler: Client has dropped the connection, cancel the query.
1193750:2023.03.22 22:54:50.477558 [ 18911 ] {5f8a4909-021c-4dca-8898-62add982d015} <Fatal> : Logical error: 'Pipeline for PushingPipelineExecutor was finished before all data was inserted'.
1193755:2023.03.22 22:54:50.479549 [ 24535 ] {} <Fatal> BaseDaemon: (version 23.3.1.1, build id: E311E03659E90DF873DD1DA003D8FC7273DFFA2F) (from thread 18911) (query_id: 5f8a4909-021c-4dca-8898-62add982d015) (query: insert into function remote('127.2', currentDatabase(), in_02232) select * from numbers(1e6)) Received signal Aborted (6)

looks irrelevant