YQ-4447 disabled thread pool in s3 by default

[GrigoriyPA]

Changelog entry

Temporary fix for: #21207

Changelog category

• Bugfix

Description for reviewers

Fix only for default s3 configuration (when external data sources and s3 are enabled)

[github-actions]

⚪ 2025-08-01 09:50:10 UTC Pre-commit check linux-x86_64-release-asan for f2697de has started.
⚪ 2025-08-01 09:50:35 UTC Artifacts will be uploaded here
⚪ 2025-08-01 09:54:28 UTC ya make is running...
🟡 2025-08-01 11:43:31 UTC Some tests failed, follow the links below. This fail is not in blocking policy yet

Test history | Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
14245	13835	0	89	297	24

🟢 2025-08-01 11:44:48 UTC Build successful.
🟢 2025-08-01 11:45:19 UTC ydbd size 3.9 GiB changed* by +19.1 KiB, which is < 100.0 KiB vs main: OK

ydbd size dash	main: 2689dea	merge: f2697de	diff	diff %
ydbd size	4 234 880 720 Bytes	4 234 900 272 Bytes	+19.1 KiB	+0.000%
ydbd stripped size	1 466 846 136 Bytes	1 466 851 608 Bytes	+5.3 KiB	+0.000%

^{*please be aware that the difference is based on comparing your commit and the last completed build from the post-commit, check comparation}

[github-actions]

🟢 2025-08-01 09:50:11 UTC The validation of the Pull Request description is successful.

[github-actions]

⚪ 2025-08-01 09:51:08 UTC Pre-commit check linux-x86_64-relwithdebinfo for f2697de has started.
⚪ 2025-08-01 09:51:21 UTC Artifacts will be uploaded here
⚪ 2025-08-01 09:54:35 UTC ya make is running...
🟡 2025-08-01 11:10:38 UTC Some tests failed, follow the links below. Going to retry failed tests...

Test history | Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
36490	33693	0	3	2766	28

⚪ 2025-08-01 11:14:07 UTC ya make is running... (failed tests rerun, try 2)
🟢 2025-08-01 11:26:59 UTC Tests successful.

Test history | Ya make output | Test bloat | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
761 (only retried tests)	646	0	0	93	22

🟢 2025-08-01 11:27:09 UTC Build successful.
🟢 2025-08-01 11:27:28 UTC ydbd size 2.2 GiB changed* by +15.3 KiB, which is < 100.0 KiB vs main: OK

ydbd size dash	main: 2689dea	merge: f2697de	diff	diff %
ydbd size	2 408 525 208 Bytes	2 408 540 880 Bytes	+15.3 KiB	+0.001%
ydbd stripped size	503 241 864 Bytes	503 247 688 Bytes	+5.7 KiB	+0.001%

^{*please be aware that the difference is based on comparing your commit and the last completed build from the post-commit, check comparation}