source-mongodb: add support for AWS DocumentDB

AWS DocumentDB is mostly MongoDB wire protocol compatible, and supports many of
the features that MongoDB does.

It's support for change streams is pretty limited though, since they don't
include a post-batch resume token, which makes them basically unusable for our
current connector.

But we can support DocumentDB with batch-mode bindings, and using a somewhat
hacky way of detecting that we are connecting to DocumentDB using a regex on the
configured address that allows the necessary TLS configuration to be set.

source-mongodb/VARIANTS

@@ -1 +1,2 @@
-source-cosmosdb-mongodb
+source-cosmosdb-mongodb
+source-amazon-documentdb

source-mongodb/discovery.go

@@ -168,7 +168,7 @@ func (d *driver) Discover(ctx context.Context, req *pc.Request_Discover) (*pc.Re
 		return &pc.Response_Discovered{Bindings: bindings}, nil
 	}
 
-	serverInfo, err := getServerInfo(ctx, client, databaseNames[0])
+	serverInfo, err := getServerInfo(ctx, cfg, client, databaseNames[0])
 	if err != nil {
 		return nil, fmt.Errorf("getting server info: %w", err)
 	}