Change database name for postgres-exporter to the gitlab gitlabhq_* database

Summary

postgres-exporter references the postgres database in /opt/gitlab/etc/postgres-exporter/env/DATA_SOURCE_NAME and should reference the gitlabhq_* database. Queries that depend on pg_class or information_schema.tables do not have visibility into the tables in gitlabhq_* if the database name is set to postgres

current value of /opt/gitlab/etc/postgres-exporter/env/DATA_SOURCE_NAME

user=gitlab-psql host=/var/opt/gitlab/postgresql database=postgres

Steps to reproduce

root@gitlab:~# gitlab-psql 
psql (10.9)
Type "help" for help.

gitlabhq_production=# select current_database(), count(1) from pg_class;
  current_database   | count 
---------------------+-------
 gitlabhq_production |  2491
(1 row)

gitlabhq_production=# select current_database(), count(1) from pg_class where relname = 'issues';
  current_database   | count 
---------------------+-------
 gitlabhq_production |     1
(1 row)

gitlabhq_production=# \c postgres
You are now connected to database "postgres" as user "gitlab-psql".
postgres=# select current_database(), count(1) from pg_class;
 current_database | count 
------------------+-------
 postgres         |   341
(1 row)

postgres=# select current_database(), count(1) from pg_class where relname = 'issues';
 current_database | count 
------------------+-------
 postgres         |     0
(1 row)

postgres=#

Change database name for postgres-exporter to the gitlab gitlabhq_* database

Summary

Steps to reproduce

What is the current bug behavior?

What is the expected correct behavior?

Relevant logs

Details of package version

Configuration details