Adds the Apache 2.0 license to allow code re-use. We've chosen this
license for this repo because:

- We don't mind people adapting and either partial or complete bits of
  code for their own projects.

- Any modifications is likely to be bespoke to their env. and needs.
  Whilst it would be nice to share around, a strong copy-left
  requirement is likely to prevent people re-using bits, which we
  wouldn't likely benefit from anyway.

- It still allows attribution, as we're just as happy to collaborate
  where we can too.

Applies SPDX identifier across the repo automatically to indicate the
Apache-2.0 license and owner