Variables can be deprecated through the `deprecated` attribute. If set the variable
will emit a diagnostic if a values is passed to it. This entails both root level and
module variables.
Outputs can be deprecated through the `deprecated` attribute as well. If set wherever
the value is used a diagnostic will be emitted. Root level outputs can not be deprecated.
The only acceptable usage of a deprecated output is another deprecated output (forwarding
the deprecation to the module user).
If modules not under your control have deprecation warnings you can add a `suppress_deprecations_warnigns`
attribute to the module call in question to silence any deeply nested warnings.
