feat: set appname for pg_stat_activity entry

[steve-chavez]

This is so select * from pg_stat_activity where application_name like '%pg_net%'; can work as usual.

[za-arthur]

Thank you! Looks good to me.
It is possible to get status of the worker by checking backend_type:

=# select datname, application_name, state, backend_type from pg_stat_activity where backend_type like 'pg_net%';
   datname    │ application_name │ state  │     backend_type
──────────────┼──────────────────┼────────┼──────────────────────
 pre_existing │                  │ (null) │ pg_net 0.12.0 worker

But I suppose altering application_name could make it more friendlier to users.

[steve-chavez]

But I suppose altering application_name could make it more friendlier to users.

Yes, this was just a nicety. I noticed pg_cron does the same.