from_dict doesn't handle `Tags` well

Specifying `Tags` for an object doesn't work with `from_dict`. It isn't a subclass of `BaseAWSObject` and doesn't have a `from_dict` method.

I think we should do something like:

```
if isinstance(prop_type, Tags):
value = Tags(**value)
```

does that sound right?

Start at the from_dict entry point and the Tags class to trace how tagged values are currently converted. Reproduce the reported failure with an object containing Tags, then add coverage showing that dictionary input is converted successfully and existing from_dict behavior remains intact.

Written by the indexing model from the issue text.