Expose Postgres database connection configuration properties including max connection lifetime

[kentbull]

Configuring the max lifetime for the Postgres database connection type, and likely all others, like maxLifetime in HikariCP would allow for regular connection cycling on a configured lifetime duration. I believe the default is "0" in the database/sql library, or infinite lifetimes.

PQ says it "Handles bad connections for database/sql" and line 727 func TestCloseBadConn seems to indicate PQ will recover from bad connections, that seem to last for an infinite timeframe, though I have seen in production stale connection pools not recycle stale connections. If we have access to the underlying configuration properties then we can manually configure the connection lifecycle.

The configuration properties I have in mind are as indicated in this article:

db.SetMaxOpenConns(25)
db.SetMaxIdleConns(25)
db.SetConnMaxLifetime(5*time.Minute)

[kentbull]

Here's the relevant code from database/sql showing that If d <= 0, connections are not closed due to a connection's age.

// SetConnMaxLifetime sets the maximum amount of time a connection may be reused.
//
// Expired connections may be closed lazily before reuse.
//
// If d <= 0, connections are not closed due to a connection's age.
func (db *DB) SetConnMaxLifetime(d time.Duration) {
	if d < 0 {
		d = 0
	}
	db.mu.Lock()
	// Wake cleaner up when lifetime is shortened.
	if d > 0 && d < db.maxLifetime && db.cleanerCh != nil {
		select {
		case db.cleanerCh <- struct{}{}:
		default:
		}
	}
	db.maxLifetime = d
	db.startCleanerLocked()
	db.mu.Unlock()
}

Looks like all we need to do is expose that API. PR incoming...