Support concat function

[inoorinoor]

Support concat function via || operator (https://ydb.tech/docs/en/yql/reference/syntax/expressions?version=v25.2)

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

In my query I encountered with such error
query: select re1_0.ID from REALM re1_0 where Unicode::ToLower(re1_0.NAME) like concat('%',Unicode::ToLower($jp1),'%')

2026-02-24 02:46:23 Caused by: tech.ydb.jdbc.exception.YdbSQLException: Cannot call 'DATA_QUERY >>
2026-02-24 02:46:23 DECLARE $jp1 AS Text;
2026-02-24 02:46:23 select re1_0.ID from REALM re1_0 where Unicode::ToLower(re1_0.NAME) like concat('%',Unicode::ToLower($jp1),'%')' with Status{code = GENERIC_ERROR(code=400080), issues = [74:2 - 74:2: Unknown builtin: concat (S_ERROR)]}
2026-02-24 02:46:23     at tech.ydb.jdbc.exception.ExceptionFactory.createException(ExceptionFactory.java:49)
2026-02-24 02:46:23     at tech.ydb.jdbc.context.YdbValidator.call(YdbValidator.java:95)
2026-02-24 02:46:23     at tech.ydb.jdbc.context.QueryServiceExecutor.executeInMemoryQuery(QueryServiceExecutor.java:264)
2026-02-24 02:46:23     at tech.ydb.jdbc.context.QueryServiceExecutor.executeDataQuery(QueryServiceExecutor.java:308)
2026-02-24 02:46:23     at tech.ydb.jdbc.impl.YdbStatementBase.executeDataQuery(YdbStatementBase.java:220)
2026-02-24 02:46:23     at tech.ydb.jdbc.impl.YdbPreparedStatementImpl.execute(YdbPreparedStatementImpl.java:144)
2026-02-24 02:46:23     at tech.ydb.jdbc.impl.YdbPreparedStatementImpl.executeQuery(YdbPreparedStatementImpl.java:121)
2026-02-24 02:46:23     at tech.ydb.jdbc.impl.YdbPreparedStatementImpl.executeQuery(YdbPreparedStatementImpl.java:43)
2026-02-24 02:46:23     at org.hibernate.sql.results.jdbc.internal.DeferredResultSetAccess.executeQuery(DeferredResultSetAccess.java:285)
2026-02-24 02:46:23     ... 31 more

Unknown builtin: concat

Issue Number: N/A

What is the new behavior?

Register new function concat that will work through pipe operator || (https://ydb.tech/docs/en/yql/reference/syntax/expressions?version=v25.2)

Other information