Fix CLI dump for external table and data source

[maybenotilya]

Changelog entry

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Changelog category

• Not for changelog (changelog entry is not required)

Description for reviewers

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[github-actions]

⚪ 2025-11-28 20:35:08 UTC Pre-commit check linux-x86_64-release-asan for cc8b723 has started.
⚪ 2025-11-28 20:35:13 UTC Artifacts will be uploaded here
⚪ 2025-11-28 20:36:32 UTC ya make is running...
🟡 2025-11-28 20:55:22 UTC Some tests failed, follow the links below. This fail is not in blocking policy yet

Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
369	362	0	7	0	0

🟢 2025-11-28 20:55:29 UTC Build successful.
🟢 2025-11-28 20:55:49 UTC ydbd size 3.8 GiB changed* by +3.4 KiB, which is < 100.0 KiB vs main: OK

ydbd size dash	main: 88eecd4	merge: cc8b723	diff	diff %
ydbd size	4 117 083 752 Bytes	4 117 087 272 Bytes	+3.4 KiB	+0.000%
ydbd stripped size	1 529 604 016 Bytes	1 529 605 680 Bytes	+1.6 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}

[Copilot]

Pull request overview

This PR fixes CLI dump functionality for external tables and external data sources by adding these entity types to the list of supported schema entry types in the database iterator.

• Adds ExternalDataSource and ExternalTable to the list of supported entry types in TDbIterator

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[github-actions]

🟢 2025-11-28 20:57:34 UTC The validation of the Pull Request description is successful.

[github-actions]

⚪ 2025-11-29 16:58:32 UTC Pre-commit check linux-x86_64-relwithdebinfo for cc8b723 has started.
⚪ 2025-11-29 16:59:48 UTC Artifacts will be uploaded here
⚪ 2025-11-29 17:01:42 UTC ya make is running...
🟢 2025-11-29 17:27:35 UTC Tests successful.

Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
2751	2742	0	0	6	3

🟢 2025-11-29 17:27:42 UTC Build successful.
🟢 2025-11-29 17:28:00 UTC ydbd size 2.3 GiB changed* by 0 Bytes, which is <= 0 Bytes vs main: OK

ydbd size dash	main: affb025	merge: cc8b723	diff	diff %
ydbd size	2 459 822 544 Bytes	2 459 822 544 Bytes	0 Bytes	0.000%
ydbd stripped size	523 880 392 Bytes	523 880 392 Bytes	0 Bytes	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}