deps,tools: add missing nghttp2 license

Add `COPYING` from `nghttp2` and register it in
`tools/license-builder.sh`.

Also run `tools/license-builder.sh` and commit the
resulting `LICENSE` file.

Ref: https://github.com/nghttp2/nghttp2/blob/master/COPYING
PR-URL: https://github.com/nodejs/node/pull/14806


Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>