Some fixes in vector index schema

[MBkkt]

Changelog category

• Not for changelog (changelog entry is not required)

Additional information

Needed for this PR: #12639
Contains such changes:

• Rename vector index impl table column constants to make them more convinient and less confusing (e.g. single constant for ParentColumn, important for future kqp rewrite rules)
• Rename __ydb_embedding column to __ydb_centroid column, because it makes more sense
• Add missed not null property for vector index impl table columns

[MBkkt]

All these variables defined in very specific namespace NKikimr::NTableIndex::NTableVectorKmeansTreeIndex

[github-actions]

⚪ 2024-12-18 13:02:17 UTC Pre-commit check linux-x86_64-release-asan for 807c812 has started.
⚪ 2024-12-18 13:02:29 UTC Artifacts will be uploaded here
⚪ 2024-12-18 13:05:29 UTC ya make is running...
🟡 2024-12-18 14:37:53 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?
13949	13840	0	50	12	47

🟢 2024-12-18 14:39:00 UTC Build successful.
🟢 2024-12-18 14:39:25 UTC ydbd size 3.6 GiB changed* by +20.5 KiB, which is < 100.0 KiB vs main: OK

ydbd size dash	main: 881ce4a	merge: 807c812	diff	diff %
ydbd size	3 894 631 112 Bytes	3 894 652 120 Bytes	+20.5 KiB	+0.001%
ydbd stripped size	1 363 862 608 Bytes	1 363 873 552 Bytes	+10.7 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}

[github-actions]

⚪ 2024-12-18 13:05:18 UTC Pre-commit check linux-x86_64-relwithdebinfo for 807c812 has started.
⚪ 2024-12-18 13:05:29 UTC Artifacts will be uploaded here
⚪ 2024-12-18 13:08:46 UTC ya make is running...
🟡 2024-12-18 14:59:56 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?
30839	27890	0	2	2830	117

⚪ 2024-12-18 15:02:40 UTC ya make is running... (failed tests rerun, try 2)
🟢 2024-12-18 15:14:57 UTC Tests successful.

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

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
164 (only retried tests)	54	0	0	0	110

🟢 2024-12-18 15:15:04 UTC Build successful.
🟢 2024-12-18 15:15:23 UTC ydbd size 2.1 GiB changed* by +224 Bytes, which is < 100.0 KiB vs main: OK

ydbd size dash	main: dbb2dc8	merge: 807c812	diff	diff %
ydbd size	2 253 790 840 Bytes	2 253 791 064 Bytes	+224 Bytes	+0.000%
ydbd stripped size	483 058 000 Bytes	483 058 064 Bytes	+64 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}