Rename two columns in pg_stat_subscription_stats.

Rename two columns in pg_stat_subscription_stats.

This patch renames the sync_error_count column to sync_table_error_count
in the pg_stat_subscription_stats view. The new name makes the purpose
explicit now that a separate column exists to track sequence
synchronization errors.

Additionally, the column seq_sync_error_count is renamed to
sync_seq_error_count to maintain a consistent naming pattern, making it
easier for users to group, and query synchronization related counters.

Author: Vignesh C <vignesh21@gmail.com>
Reviewed-by: Peter Smith <smithpb2250@gmail.com>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Discussion: https://postgr.es/m/CALDaNm3WwJmz=-4ybTkhniB-Nf3qmFG9Zx1uKjyLLoPF5NYYXA@mail.gmail.com