Make the errcontext message in logical replication worker translation friendly.

Make the errcontext message in logical replication worker translation friendly.

Previously, the message for logical replication worker errcontext is
incrementally built, which was not translation friendly.  Instead, we use
complete sentences with if-else branches.

We also remove the commit timestamp from the context message since it's
not important information and made the message long.

Author: Masahiko Sawada
Reviewed-by: Takamichi Osumi, and Amit Kapila
Discussion: https://postgr.es/m/CAD21AoBarBf2oTF71ig2g_o=3Z_Dt6_sOpMQma1kFgbnA5OZ_w@mail.gmail.com