This introduces an `acl` package in `internal` which globally configures
the allowance to namespaced references, instead of having to pass on a
variable everywhere.
For the sake of security, the default behavior of the package itself is
to _not_ allow cross namespace references. However, the behavior of the
controller remains unchanged, and the configuration flag still enables
the allowance by default.
Signed-off-by: Hidde Beydals <hidde@hhh.computer>