Ensure NOTICE and LICENSE files are up to date and bundled with packaged code

[JoshMock]

This repo's NOTICE file is out of date and needs to reflect Elastic's latest requirements and an accurate date range.

We also need to add a NOTICE.txt file to @elastic/transport.

Both packages also need to be configured to ensure that both LICENSE and NOTICE files are included in the bundled code that is published to npm, using the ``files` configuration.