alpha9 release

Even though almost nothing has changed, the switch from openssl to
rustls should make some users a lot happier (e.g. those using CloudShell
where you have to install openssl11-libs everytime your shell
unsuspends).

I did consider building openssl statically, but it seems the community
has chosen rustls by default (e.g. https://rusoto.org/lambdas.html
recommands it, among other resources).

CHANGELOG.md

@@ -1,6 +1,6 @@
 # Changelog
 
-## [2.0.0-alpha9] - [Unreleased]
+## [2.0.0-alpha9] - 2021-05-06
 
 ### Changed