Linters for Envbuilder aren't catching some common concerns that we have

Suggestion: It's best practice for exported functions to have documentation (`// EnvWithBuildSecretPrefix ...`). It's part of the original Go linter (https://pkg.go.dev/github.com/golang/lint) and [CodeReviewComments](https://go.dev/wiki/CodeReviewComments#doc-comments)/[Effective Go](https://go.dev/doc/effective_go#commentary), so a bit surprising that it's not caught.

```
❯ golint ./...
envbuilder.go:43:2: a blank import should be only in a main or test package, or have a comment justifying it
devcontainer/devcontainer.go:34:6: exported type Spec should have comment or be unexported
devcontainer/devcontainer.go:50:6: exported type LifecycleScripts should have comment or be unexported
devcontainer/devcontainer.go:57:6: exported type BuildSpec should have comment or be unexported
devcontainer/devcontainer.go:78:1: exported function SubstituteVars should have comment or be unexported
devcontainer/script.go:16:6: exported type LifecycleScript should have comment or be unexported
devcontainer/script.go:21:1: exported method LifecycleScript.IsEmpty should have comment or be unexported
```

It seems `golint` is marked deprecated in `golangci-lint` though, so I guess the alternative linters aren't enforcing this rule. 😔 I always found it slightly annoying but ultimately worth the annoyance 😄.

_Originally posted by @mafredri in https://github.com/coder/envbuilder/pull/391#discussion_r1818991909_

---

There seem to be some linting rules that we'd value here. Two of them are:
* Tests should run in parallel when they can
* Exported functions should be documented

There may be others. It would be worth checking coder/coder's linting config to see what else we're missing. We should add the linters we deem important and ensure the project conforms to them.

Beginne mit der Überprüfung der Linting-Konfiguration und vergleiche sie mit der Konfiguration von coder/coder. Führe anschließend den aktuellen Linter gegen envbuilder.go, devcontainer/devcontainer.go und devcontainer/script.go aus. Füge die vereinbarten Regeln für die Dokumentation exportierter Elemente und parallelisierbare Tests hinzu, behebe die daraus resultierenden Verstöße und stelle sicher, dass die Lint- und Testbefehle des Projekts erfolgreich ausgeführt werden.

Vom Indexierungsmodell aus dem Issue-Text verfasst.