sql/vecindex: support vector indexes in metadata tables

[HasithDeAlwis]

Closes #152101
Introduce vector index support into SQL metadata by extending catalog tables, internal metadata views, and adding validation tests.

Implementation:

• Added is_vector boolean column to crdb_internal.table_indexes to identify vector indexes alongside existing index type flags
• Added "vector" access method entry to pg_catalog.pg_am with appropriate PostgreSQL-compatible metadata for vector indexes

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[cockroach-teamcity]

This change is