feat: ensure e2e projects have implicitDependencies declared

[getlarge]

User story

When using the plugin, the e2e project (envProject) should have implicitDependencies declared where (at least) the project being tested is listed.
This is a requirement to detect which files to use as cache inputs.

Acceptance criteria

• Add an e2e test with a project that has empty implicit dependencies and watch the plugin failing|skipping.

Implementation details

In #48, I added a warning when implicitDependencies are empty, we could go further and skip the target's generation.