feat(ir): Add CLI version and definition URL

[amckinney]

Overview

This adds the cliVersion and definitionUrl property to the IR's SourceConfig type so that the generator has access to additional source information during generation. Note that this means the SourceConfig now contains the following information:

1. The CLI version
2. The Fern definition files
3. The source files used to create the Fern definition (i.e. AsyncAPI, OpenAPI, etc files), if any.

All of this information has to do with the "source" of the IR, so it feels natural to include them all alongside one another.

Implementation

This effectively consolidate the fields that are passed to the remote code generation service (link) into the IR so that we can rely on the generator-agent for more functionality.

The IR changes are included as optional parameters in IRv53 for now, but they should later be marked as required in a future IR change (as noted in the CHANGELOG.md).