Add db connection monitoring

[marcmengel]

We could have the metacat daemon polling and logging information like database connections, and slow queries
with variations on queries to pg_stat_activity in Postgresql:
SELECT client_addr, client_start, query_start, query FROM pg_stat_activity WHERE datname = 'hypot_dm_dev' and state='active' ;
we could then report connection counts to Landscape and long-running queries.
Or perhaps
'select client_addr, count(*) from pg_stat_activity WHERE datname = 'hypot_dm_dev' group by client_addr;'

Sample of getting this from psql:

dune_metadata_prd=> select client_addr, count(*) from pg_stat_activity WHERE datname = 'dune_metadata_prd' group by client_addr;
   client_addr   | count 
-----------------+-------
 131.225.67.132  |     4
 131.225.67.133  |     4
 131.225.67.247  |     1
 131.225.108.42  |     1
 131.225.240.229 |     4
 131.225.240.230 |     4
dune_metadata_prd=> select client_addr, count(*) from pg_stat_activity WHERE datname = 'dune_metadata_prd' and state='active' group by client_addr;
  client_addr   | count 
----------------+-------
 131.225.67.247 |     1

Note that we always see ourselves in the results (dunegpvm02 = 131.225.67.247 in this example), and so we should
not count our connection in the results...

[marcmengel]

One more example query:

dune_metadata_prd=> select client_addr, state, count(*) from pg_stat_activity WHERE datname = 'dune_metadata_prd'  group by client_addr,state;
   client_addr   |        state        | count 
-----------------+---------------------+-------
 131.225.67.132  | idle                |     3
 131.225.67.132  | idle in transaction |     2
 131.225.67.133  | idle                |     4
 131.225.67.247  | active              |     1
 131.225.108.42  | idle                |     1
 131.225.240.229 | idle                |     4
 131.225.240.230 | active              |     1
 131.225.240.230 | idle                |     4
 131.225.240.230 | idle in transaction |     1
(9 rows)