Manually specify shape renames for AWS services

[kggilmer]

#177022993 introduced renaming of model types that conflict with Kotlin builtin types (e.g. Unit).

It would be better to fail the build and require a manual customization to rename these types for following reasons:

1. Having the rename implemented in code opens us up to accidentally changing the rules of that rename and breaking customers. This is hard to detect since it all just happens automatically.
2. We can provide better names for these renames. Like point (1) by having the rename rule as code we can only follow a particular pattern but we can't actually guarantee that the renamed type comes out sensible. By manually choosing the name we can provide a better customer experience.

Smithy 1.6.1 has support for this directly: https://github.com/awslabs/smithy/pull/721/files#diff-7d898edc06a29654f5803d197345007c92fd0306f1f94a0eeaacfcab1469de38

internal id: 177144277

[aajtodd]

We have a mechanism now to implement this. See here for an example.

The integration that auto renames conflicts with builtin types is defined here