d/aws_route_table: AWS Wavelength support.

Acceptance test output:

$ make testacc TEST=./aws/ TESTARGS='-run=TestAccDataSourceAwsRouteTable_'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./aws -v -count 1 -parallel 20 -run=TestAccDataSourceAwsRouteTable_ -timeout 120m
=== RUN   TestAccDataSourceAwsRouteTable_basic
=== PAUSE TestAccDataSourceAwsRouteTable_basic
=== RUN   TestAccDataSourceAwsRouteTable_main
=== PAUSE TestAccDataSourceAwsRouteTable_main
=== CONT  TestAccDataSourceAwsRouteTable_basic
=== CONT  TestAccDataSourceAwsRouteTable_main
--- PASS: TestAccDataSourceAwsRouteTable_main (19.21s)
--- PASS: TestAccDataSourceAwsRouteTable_basic (33.59s)
PASS
ok  	github.com/terraform-providers/terraform-provider-aws/aws	33.695s

website/docs/d/route_table.html.markdown

@@ -68,6 +68,7 @@ When relevant, routes are also exported with the following attributes:
 For destinations:
 
 * `cidr_block` - CIDR block of the route.
+* `destination_prefix_list_id` - The ID of a [managed prefix list](ec2_managed_prefix_list.html) destination of the route.
 * `ipv6_cidr_block` - IPv6 CIDR block of the route.
 
 For targets: