KeepAlive configuration parameter is ignored - connections grow with jobs count

[vladimirfx]

Use case:

We have 10+ jobs with different schedules pointing to one PostgreSQL instance. All those jobs are configured with keepalive: false but we see established connections equal to the number of jobs all the time.

Research:

Searching sources I've found that the keepalive parameter is not used.

Alternative solution:

Implement named reusable connections: #90