feat: Reference internal-tls TF file in docs

[MichaelThamm]

Issue

This moves us in the direction of infaliable docs. We want to have our TF modules in docs tested so that we have guarantee we are not misleading our users.

In tandem with these docs:

• feat(doc): add install guide #289
• chore: update cos-lite tutorial #323

Solution

In the Deploy COS Lite using Terraform section you can see the HCL broken up into 3 parts:

this is because the first and last part are being tested by our tests/integration and are infallible.

This is a step in the right direction, but is not the complete "infallible" story. The problem is that the itest requires Jubilant to create temp models, however the user is expected to create them in the tutorials. This is why I added a cos-meta.tf file in the docs/tutorials dir so we can reference this in all our docs for TF API usage. This also means that if we change the model creation UX in TF then we only need to update this in one place.

Checklist

• I have added or updated relevant documentation.
• PR title makes an appropriate release note and follows conventional commits syntax.
• Merge target is the correct branch, and relevant tandem backport PRs opened.

Context

Eventually we need to conform to the CC008 spec:

Juju models are defined in Product modules, and then fed to the various charm modules and component models that consume juju model UUIDs as inputs. Since product modules may generally be user-facing, product teams may decide to expose the model name as input variable to either create or consume a model. The TF resource (either juju_model resource or data juju model) is then used to pass the related UUID to charm and component modules.

This will simplify the docs and make them truly "infallible".

Testing Instructions

Upgrade Notes