Add blueprint for charms and terraform

[lucabello]

We should add a blueprint for charms and for Terraform module. The charm blueprints should include the Terraform recipes (as in, the charm blueprint should use the Terraform blueprint), or just replicate them.

The charm blueprints should be something like:

lock:
alias fmt := format
format:
lint:
  do both linting and static check
lint-todos  # name up for discussion
unit:
integration:

The terraform one:

terraform-lint:
  lint both module and config is updated, provides/requires endpoitns, run terraform validate
terraform-format:
  format the module and generate the config

---

From #380 : Add a lint-todo environment to tox

The name of the environment is still up for debate.

This comes from https://github.com/canonical/observability-team/issues/124

We don't want to add this check to tox -e lint because it would prevent integration tests from running.

This new command should fail if:

1. FIXME is ANYWHERE in the linted code (src/ and any owned charm libs)
2. TODO is not immediately followed by an issue (i.e. TODO: <link>)

Note that this has implications on other teams using our CI, and we'd need to make sure this check is optional or opt-in.

[lucabello]

Supersedes:

• feat: TF CI alertmanager-k8s-operator#350
• Move Terraform lint, format, and validate Just recipes to central workflows in the observability repo observability-stack#39
• Add a lint-todo environment to tox #380