Add a GitHub issue template for questions

Add a GitHub issue template for questions

Actually, we would rather see general questions posted to the
openssl-users mailing list. But habits have changed and more and
more users ask questions on GitHub. Many of them are currently tagged
as bug reports or feature requests, because there is no appropriate
template for questions. This commit adds the missing template.

This template automatically adds the [issue: question] label.

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/10051)