auth_file for plaintext passwords

lib/bouncer/backends/v0/accept.go

lib/gat/configs/pgbouncer/config.go

lib/gat/pool.go

lib/util/encoding/ini/readfile.go

lib/util/encoding/ini/unmarshal.go

lib/util/encoding/ini/unmarshal_test.go

lib/util/encoding/userlist/unmarshal.go

pgbouncer.ini

userlist.txt