feat: detect "vendor" folder for local builds

[boojamya]

When using the --local flag, this adds support for chains that choose to vendor all their Go dependancies.

Also updates docker.

[vimystic]

Question: The vendor dir will be something one would locally use with their own dependancies?
i.e : there is no expectation of a vendor dir living in the repo, correct?

[boojamya]

running go mod vendor will download and place all of the project dependancies in a "vendor" folder. Running go build -mod=vendor will tell go to build the project from the vendor folder instead of fetching all deps from the internet.

I think it is safe to assume that go projects should not have a vendor folder unless they are "vendoring" dependencies.