Refactor code handling the names of files loaded in hba.c

This has the advantage to limit the presence of the GUC values
hba_file and ident_file to the code paths where these files are loaded,
easing the introduction of an upcoming feature aimed at adding inclusion
logic for files and directories in HBA and ident files.

Note that this needs the addition of the source file name to HbaLine, in
addition to the line number, which is something needed by the backend in
two places of auth.c (authentication failure details and auth_id log
when log_connections is enabled).

While on it, adjust a log generated on authentication failure to report
the name of the actual HBA file on which the connection attempt matched,
where the line number and the raw line written in the HBA file were
already included.  This was previously hardcoded as pg_hba.conf, which
would be incorrect when a custom value is used at postmaster startup for
the GUC hba_file.

Extracted from a larger patch by the same author.

Author: Julien Rouhaud
Discussion: https://postgr.es/m/20220223045959.35ipdsvbxcstrhya@jrouhaud

Author: michaelpq

src/backend/libpq/auth.c

@@ -307,8 +307,9 @@ auth_failed(Port *port, int status, const char *logdetail)
 			break;
 	}
 
-	cdetail = psprintf(_("Connection matched pg_hba.conf line %d: \"%s\""),
-					   port->hba->linenumber, port->hba->rawline);
+	cdetail = psprintf(_("Connection matched %s line %d: \"%s\""),
+					   port->hba->sourcefile, port->hba->linenumber,
+					   port->hba->rawline);
 	if (logdetail)
 		logdetail = psprintf("%s\n%s", logdetail, cdetail);
 	else
@@ -365,7 +366,7 @@ set_authn_id(Port *port, const char *id)
 					   "(%s:%d)",
 					   MyClientConnectionInfo.authn_id,
 					   hba_authname(MyClientConnectionInfo.auth_method),
-					   HbaFileName, port->hba->linenumber));
+					   port->hba->sourcefile, port->hba->linenumber));
 	}
 }