Enhance exporter to capture 'show clients'

[valcocer-d]

Notice that the exporter just expose stats data. Any plans/enhacements to provide output from show clients so we can get more details about clients connecting to pgbouncer

[valcocer-d]

SHOW CLIENTS
type
C, for client.
user
Client connected user.
database
Database name.
replication
If client connection uses replication. Can be none, logical or physical.
state
State of the client connection, one of active, waiting, active_cancel_req, or waiting_cancel_req.
addr
IP address of client.
port
Source port of client.
local_addr
Connection end address on local machine.
local_port
Connection end port on local machine.
connect_time
Timestamp of connect time.
request_time
Timestamp of latest client request.
wait
Current waiting time in seconds.
wait_us
Microsecond part of the current waiting time.
close_needed
not used for clients
ptr
Address of internal object for this connection. Used as unique ID.
link
Address of server connection the client is paired with.
remote_pid
Process ID, in case client connects over Unix socket and OS supports getting it.
tls
A string with TLS connection information, or empty if not using TLS.
application_name
A string containing the application_name set by the client for this connection, or empty if this was not set.
prepared_statements
The amount of prepared statements that the client has prepared