Allow for different vets-website build targets in next-build

[tjheffner]

Requirements

In #14974, we introduced vets-website assets to next-build. This uses the localhost build of vets-website. This is good, but we need to get different build types available for different environments, or testing locally. i.e --buildtype=vagovprod as seen in vets-website.

The available buildtype options for vets-website are:
localhost
vagovdev
vagovstaging
vagovprod

Acceptance criteria

Beta Give feedback

1. Vets-website assets can be sourced from any vets-website build type, not only localhost.
2. Tugboat builds as expected without errors and all assets present using a non-localhost vets-website buildtype. (vagovprod? vagovdev?)

Background & implementation details

The symlink setup will likely need to be adjusted, both locally and for different CI environments depending on the buildtype used. vets-website outputs to different directories based on the build type.

e.g. with localhost it outputs to vets-website/build/localhost/generated. With vagovprod, that directory updates to vets-website/build/vagovprod/generated.

next-build will need to source the assets from next-build/public/generated no matter the build type. We may need to re-build vets-website & move the assets vs symlinking directly to the generated output specific to localhost. This would have the side effect of adding vets-website build times to most of our local static builds. For my machine, that is 6 minutes of additional build time.

webpack 5.76.0 compiled with 2 warnings in 367955 ms
./script/../build/vagovprod/generated/vendor.entry.js -> ./script/../build/vagovprod/generated/shared-modules.entry.js
✨  Done in 372.31s.

[tjheffner]

content-build downloads assets each run in this way, this is probably faster than doing a full vets-website build
https://github.com/department-of-veterans-affairs/content-build/blob/main/src/site/stages/build/plugins/download-assets.js
https://github.com/department-of-veterans-affairs/content-build/blob/main/src/site/constants/buckets.js

locally we would still want to symlink to the adjacent directory so local changes could be tested easily