Add license to composer templates

This is probably the right version.

Seems pretty straight forward

xjm → credited catch → .

xjm → credited hestenet → .

@hestenet, @catch, @drumm, and I discussed and agreed on this approach in Slack.

I have not reviewed the MR myself as yet.

Reviewed by diffing the added licenses against core/LICENSE.txt and confirming they were identical. These are the only two templates in core; I know because they talk to me every time I tag a release.

Committed to 11.x. I did not backport it to 11.2.x because a change to the scaffolding is, technically, slightly disruptive. In this case, very slightly -- although from another perspective it's actually changing how core-recommended is officially licensed so that's not nothing. Leaving PTBP for now since @phenaproxima originally asked about this issue and I want to make sure it's not a contrib blocker of some kind that we should backport prior to 11.2.0.

Per @phenaproxima:

We don’t “need it”, as such; on this point, we intend to follow core’s lead.
So we just care that core chooses an approach. It’s okay to not backport.

Committed to Drupal CMS 2.x in 311224b and cherry-picked to 1.2.x in d7066cf.

Confirmed that made it through to https://github.com/drupal/recommended-project & https://github.com/drupal/legacy-project

That also means we could add a README.md to each, so anyone who lands on the GitHub repo has some explanation.