bitrot updates

The bitrot.js script should get some updates:

1. update to work again after updates to the .tav.yml format (using the recent version ranges mode)
2. add support for checking for newer Lambda runtimes (https://docs.aws.amazon.com/lambda/latest/dg/lambda-runtimes.html#runtimes-supported). See https://github.com/elastic/apm-agent-nodejs/issues/4033 where it currently takes a customer or someone noticing that we are out of date.
3. Run bitrot regularly (in GH actions?) so that we see the out-of-date state. Perhaps in GH actions with a slack notification.