Finalize devcontainer.json search

[code-asher]

I tested all the scenarios I could think of and everything seems to be working as expected. Really would be ideal to write tests but I am not sure how to go about mocking a provider and URL reader and all that.

• different branches (although of course this will not work once we actually pass to VS Code)
• no devcontainer anywhere
• add devcontainer after (seems to refresh every two minutes)
• .devcontainer.json
• .devcontainer/devcontainer.json
• .devcontainer/nested/devcontainer.json
• test1/.devcontainer/devcontainer.json (monorepo where test1 is a project, of course this will not actually work in VS Code)
• test3 (project in the same monorepo, but without devcontainer)

Backstage seems to run the processor every two minutes. Not sure if this is configurable. We should probably do caching with ETags.

For https://github.com/coder/backstage.cdr.dev/issues/47, but technically does not close the issue since it wants a POC for three providers, which I imagine we can set up in the backstage.cdr.dev deployment.

[code-asher]

Hmm looks like CI struggles when building the plugins separately because yarn tsc requires all the plugins to be built...we have to run yarn tsc to build a plugin and I guess it runs from the root. But I suppose it is not related to this PR so I will merge and fix it in another.

~There must be a way to build a single plugin without having to build them all...also how was this even working before if yarn tsc requires yarn build which requires yarn tsc?~

Edit: was wrong about this, the problem was that it could not find the types because the entry point in the package.json had been changed in another PR to the built files rather than pointing directly at the source TypeScript files, making it appear as though the plugin needed to be built first.