Add config table

[davidfetter]

Per conversation with and thanks to @fabriziomello, modify pgbouncer_wrapper as folllows:

• Add a config table with (bouncer_name TEXT PRIMARY KEY, bouncer_connect_string TEXT, active BOOLEAN NOT NULL DEFAULT true);
• Instead of creating a server, do a LATERAL JOIN to the config table with the connect string instead of the server that's been dropped. The view needs to include the bouncer_name column at a minimum to disambiguate info from multiple bouncers.
• This way, it's as easy to monitor N pgbouncers as it is to monitor one.

[fabriziomello]

Example:

CREATE TABLE pgbouncer.instances (
    bouncer_name TEXT PRIMARY KEY,
    bouncer_connect_string TEXT,
    active BOOLEAN NOT NULL DEFAULT true
);

INSERT INTO pgbouncer.instances VALUES ('pgbouncer1', 'host=/tmp port=6432 dbname=pgbouncer');

CREATE OR REPLACE VIEW
  pgbouncer.clients
AS
SELECT
  _.type, _."user", _.database, _.state, _.addr, _.port, _.local_addr,
  _.local_port, _.connect_time, _.request_time, _.wait, _.wait_us,
  _.close_needed, _.ptr, _.link, _.remote_pid, _.tls 
FROM
  pgbouncer.instances
JOIN LATERAL
  dblink(instances.bouncer_connect_string, 'show clients'::text) 
  AS _(type text, "user" text, database text, state text, addr text, port integer, local_addr text, local_port integer, connect_time timestamp with time zone, request_time timestamp with time zone, wait integer, wait_us integer, close_needed integer, ptr text, link text, remote_pid integer, tls text) ON true
WHERE
  instances.active IS TRUE;