There are some cases where an attribute is completely removed from OTEL and has no direct replacement.
This is rare but can happen with attributes that are not stabilized.

For example, see the deprecated Gen AI attributes.
Some of them were deprecated and have no direct replacement.
It's suggested to use e.g. gen_ai.input.messages instead, which doesn't have the same semantic meaning and also requires a different format for attribute values.

We wouldn't want to mark e.g. gen_ai.input_messages as a replacement for gen_ai.prompt, as the former is more general and requires a different format for the values.

This extends the schema so that deprecation.replacement is nullable, allowing us to represent those cases.

Also fixes the type in scripts to correctly match the schema.