The sdk version in the shrinkwrap already
supports setting tags by commit hashes and as a
result this already works in the cli as of v11.9.6.
This PR just adds some docs and some extra
handling when the commit param prefix is all
numeric.
Resolves: #1064
Change-type: minor
Signed-off-by: Thodoris Greasidis <thodoris@balena.io>