add end-to-end C# update runner

[brettfo]

Add an option for the NuGet updater to handle the entire update process, from git clone all the way through mark_as_processed.

This is necessary because the concept of a dependency according to MSBuild/NuGet is nothing like the concept of a dependency for dependabot-core and it would require a huge rewrite of a bunch of the common code, which really means a rewrite of all 20+ updaters, so this is the best way forwards. The short version for why NuGet is so different: MSBuild allows arbitrary directory crawling and each dependency found could be top-level or transitive and each one could have different updatability semantics based on the project's TFM and/or NuGet.Config. Because of all of this, the NuGet updater needs to check every single dependency for upgradability; we can't do one big update check.

The new behavior has been placed behind an experimental flag nuget_native_updater. To enable this, the bin/run script was renamed to bin/run-original (only in this image) and a new bin/run checks the experiment flag in the job file and does the appropriate thing. To accomplish this, the Linux command jq was added to the image to query the job.json file for the flag. Powershell was also added as there's a new main.ps1 that serves as the entrypoint. This was placed in a Powershell script because it makes it easy to test the clone and SDK installation on both Linux and Windows.

The new RunWorker class is a simple wrapper around DiscoveryWorker, AnalyzeWorker, and UpdateWorker and the only change to those three classes was to add an overload that takes and returns the object files directly, instead of requiring (de)serialization to/from disk. The old behavior remains unchanged. The actual body of RunWorker is fairly straightforward; the bulk of new lines in this PR is to support the object model required for the HTTP API calls (e.g., create_pull_request, mark_as_processed, etc.)

The only scenario covered by this code is very narrow and will fail in weird ways for the vast majority of update operations, but I wanted to get this work reviewed and merged so it can be slowly iterated on.

In this PR I'm primarily looking for feedback on the architecture/implementation of main.ps1 and RunWorker.cs; the rest is mainly plumbing code.

[NomadsComputerllc]

Tahnks

[ByAgenT]

LGTM, left a few extra questions for my learning and better understanding

[willibrandon]

Is this supposed to work when central package management is enabled? I’m seeing the version failing to be located in that scenario.

[andrcuns]

FYI, this breaks ability to build nuget ecosystem docker image for arm64 arch because there is no powershell package it looks like.