pgAdmin 4: libpq uses the pgAdmin service account's own password file and client certificate

When a server in pgAdmin 4 had no password file, client certificate or client key configured, or the configured one could not be found, pgAdmin left the parameter out of the connection and libpq fell back to the defaults of the operating-system account running pgAdmin: ~/.pgpass, ~/.postgresql/postgresql.crt and postgresql.key, or PGPASSFILE, PGSSLCERT and PGSSLKEY. In server mode any user could therefore connect to a server with the service account's saved passwords or client certificate, and supplying only a copy of its public certificate was enough for libpq to pair it with the service account's private key. A pg_service.conf entry, or a maintenance database name read as a connection string by pg_dumpall, could bring the same files back for the utilities.

The fix gives each of these parameters a value in server mode, the user's own file or otherwise a path that can never be opened, in the connection string, in the environment of the utilities and in the --dbname connection string that ranks above a service entry. Desktop mode is unchanged.

This issue affects pgAdmin 4: before 9.19.