Just the image, cache and variables.

At this point, it's already processed by GitLab CI so there's little
point in running the same thing again.

The pre-commit ci-image doesn't have the Terraform CLI, but it can be
downloaded in the before_script part so it's not an issue.

This reverts commit 35a24a67. There's an
issue with pre-commit now, the way it gets the container ID is
incorrect. I'll open an issue and file a PR.

The issue is reported to have been solved.

Conflicts with other templates.

- Set a default TF_ROOT and use it.
- Use a template job to keep it DRY.

Was part of debugging the CI linter. Not useful anymore.

Fix the breaking hook as well.

All templates need at least a single job (not a template job) in them.
Instead of copying and pasting.

No need to wait for other jobs to finish.

Until I add Terraform to the image or something.

The linter can't handle it without a project, but it requires setting a
token and I'm fed up with it. If it's not useful as a git hook before
pushing, there's no point in running it in the CI (the CI wouldn't work
if the file is invalid).

Notify me on failure.

It's done with the pull job and it makes the run job faster.

The end goal is pulling and building in parallel and then deployment is
shorter.

This reverts commit d148398f.

"-parallel option is deprecated and will be removed in future versions."

Specifically for GitLab, which takes a long time not only to start but
finish its setup process and until it does it returns a 502. Eventually
it does finish and is healthy but the job already failed.

The job is now hidden, so you can base on it and set a proper script to
run the CLI.

When building ci-images, images on the host are sometimes (in the case
of the docker image, always) pulled from the registry (overwriting the
tag) but before pushing. So the image pushed is that pulled just now.
Instead save the build hash (and pretty much everthing else) and re-tag
before pushing (using the hash so it's the right image). While at it,
unify the Docker push jobs (the Docker Hub and the personal registry
one).