✨ feature: integrate SSL mode for PG connections (#77)

Right now, the default connection for postgres is `disable`. Some
databases require `verify` or even `required`.
This PR introduces a new implementation that allows the user to override
the `disable` mode. The PR keeps a backwards compatible config entry, that
sets the default behavior to `disable` if it's missing.

postgres/README.md

@@ -47,6 +47,7 @@ store := postgres.New(postgres.Config{
 	Table:           "fiber_storage",
 	Reset:           false,
 	GCInterval:      10 * time.Second,
+	SslMode:         "disable",
 })
 ```
 
@@ -93,6 +94,11 @@ type Config struct {
 	//
 	// Optional. Default is 10 * time.Second
 	GCInterval time.Duration
+
+	// The SSL mode for the connection
+	//
+	// Optional. Default is "disable"
+	SslMode string
 }
 ```
 
@@ -105,5 +111,6 @@ var ConfigDefault = Config{
 	Table:           "fiber_storage",
 	Reset:           false,
 	GCInterval:      10 * time.Second,
+	SslMode:         "disable",
 }
 ```