chore: add MutagenSdk project

[deansheather]

Contains a gRPC client for mutagen's synchronization API.

All required .proto files are vendored using a new script Update-Proto.ps1, which finds all required files by scanning import directives.

The vendored files are modified to add csharp_namespace and a MIT license header from mutagen.

Example usage:

using var client = new MutagenClient(@"C:\Users\dean\.mutagen");
var res = await client.Synchronization.ListAsync(new ListRequest
{
    Selection = new Selection
    {
        All = true,
    },
});

foreach (var state in res.SessionStates)
    Console.WriteLine(state);

Close coder/internal#378

[spikecurtis]

Few nits and suggestions inline

[spikecurtis]

We should use Coder's fork: https://github.com/coder/mutagen

Unfortunately, we are going to have to modify Mutagen and build our own releases to work around the SSH directory bug.

[deansheather]

We don't have a v0.18.1 tag in our fork. We probably need to resync it so we get all of the tags etc.

[deansheather]

Once we sort out the tags I'd be down to fix this in a follow up

[spikecurtis]

man, PowerShell is so much nicer than bash

[deansheather]

isn't the throw/try/catch/finally stuff just the best! I just wish they didn't go whole hog on making their own (usually worse) version of utilities that are available on Linux. At least curl.exe is available or I would cry

[deansheather]

@spikecurtis the Join-Path fix was added in Powershell 6.0 but Windows 11 ships with 5.1 (or at least that's what I have installed). It's like macos vs linux bash all over again