Rename sync_error_count to tbl_sync_error_count in subscription statistics

Hi,

This patch proposes renaming a column in the view
pg_stat_subscription_stats to disambiguate between table sync and
sequence sync error counts. With the introduction of
seq_sync_error_count, the existing column name sync_error_count
becomes ambiguous, it's unclear whether it refers to tables,
sequences, or both. Renaming it to tbl_sync_error_count makes the
meaning explicit: it represents errors that occurred during table
synchronization. This helps users avoid confusion when interpreting
the view's output. These changes were also suggested by Amit's first
comment at [1] and Peter's fourth comment at [2].
Thoughts?

Since an existing column is being renamed, this change should also be
mentioned in the release notes so that users can update any scripts or
monitoring queries that reference it.

[1] - https://www.postgresql.org/message-id/CAA4eK1LB7u2KQLRFh6xfTSpEB-8gbpR%3DhqzFOfL9Z1R8rj7Q5g%40mail.gmail.com
[2] - https://www.postgresql.org/message-id/CAHut%2BPtoLN0bRu7bNiSeF04dQQecoW-EXKMBX%3DHy0uqCvQa8MA%40mail.gmail.com

Regards,
Vignesh