Add system Nexus WIT operation metadata

[tconley1428]

What changed

• Adds generation step for producing/updating WIT files for exposed API definitions.
• Documents that Rust is required when running make because system Nexus WIT generation installs and runs nexus-api-gen.

[Sushisource]

Is this PR gonna have the check that new things were added or is that a follow up PR?

[tconley1428]

It already does! The API repo already checks for any dirty diff after the makefile build.

[Sushisource]

It already does! The API repo already checks for any dirty diff after the makefile build.

Aaaa, how about that then. Nice. What about manual changes to the output though? Isn't it going to complain about a diff there and we need some way to indicate it's OK?

[tconley1428]

The make command actually does a merge operation into the output rather than fully regenerating. It will leave customizations in place. There might be some teething with that but it has been working so far.

[tconley1428]

You can tell by the fact that this heavily customized output is not failing the diff check.