capture and report job deserialization errors

[brettfo]

The job.json file is passed to all update steps which means we need to be able to report all parsing errors as they occur.

Originally this work started because a requirement was specified in the job file that could not be parsed, so part of this PR is to return the well-known error illformed_requirement, represented as BadRequirementError.

Most of this PR was to make testing possible, but ultimately it comes down to 2 major changes:

1. For the current hybrid Ruby/C# updater, only validate and report job file parsing errors in the discover command. All subsequent commands also parse the job file, but any failure to parse is fatal so we only need to actually report it there; all other instances can assume it's acceptable.
2. For the new end-to-end updater, the clone command is the first time the job file is parsed, so the error handling was expanded there to specifically report the parse error and fail the entire update process.

While performing some manual tests, I discovered that the shape of the error objects returned by the end-to-end parser wasn't always correct, so I checked in the dependabot/cli repo to ensure the errors had the correct shape and added serialization tests for all error types to ensure this doesn't regress.

[brettfo]

This block of code already existed in updater_error_details but this error occurs during the fetch phase of a NuGet update so it was simply copied here, too. This is a well-known error with a known shape.