nss: Create a nss database for agl-driver user

The change creates an empty db and allows other recipes
to add their own certificates when needed.

It will be needed by kuksa-val recipe for adding its root
CA certificate that will fix CA validation issues that are
happening on chromium.

v2 (jsmoeller): convert to own recipe to avoid modifying nss itself

Bug-AGL: SPEC-4599
Signed-off-by: Roger Zanoni <rzanoni@igalia.com>
Signed-off-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
Change-Id: I5a5e4ff24cb640580cff4c609ee6293acae64487