sql: improve SHOW TABLES to show row count

[lnhsingh]

PR: cockroachdb/cockroach#52203

From release notes:

Modified SHOW TABLES to return estimates of the number of rows in each table. The new column's name is estimated_row_count. The number of rows is taken from the system.table_statistics table (via crdb_internal.table_row_statistics, which shows only tables accessible to the current user). [#52203][#52203] {% comment %}doc{% endcomment %}