chore(terraform): update terraform modules to latest standards

[jansdhillon]

Summary

This PR aligns the Terraform modules with the team's latest standards.

Changes

• terraform/charm/versions.tf: Updated required_version from >= 1.10 to ~> 1.12 and juju provider to ~> 1.0
• terraform/product/modules/landscape-scalable/versions.tf: Same version updates
• terraform/.tflint.hcl: Added tflint config at terraform root with terraform_required_version rule enabled (as per standard)
• renovate.json: Added with charmhub custom datasource for automated terraform revision tracking (renovate will auto-update charm revision numbers in .tftest.hcl files)
• terraform/charm/tests/main.tftest.hcl and terraform/charm/tests/setup/main.tf: Added integration test setup for the charm module
• terraform/product/modules/landscape-scalable/tests/main.tftest.hcl and tests/setup/main.tf`: Added integration test setup for the product module
• terraform/charm/outputs.tf: Fixed copyright year typo (2026 → 2025)
• terraform/charm/README.md and product README: Updated version constraint in auto-generated docs section

Missing (requires workflow scope on token)

The following file could not be pushed due to token permission limitations and needs to be added manually:

.github/workflows/test_terraform_modules.yaml:

# Copyright 2025 Canonical Ltd.
# See LICENSE file for licensing details.

name: Terraform modules tests

on:
  workflow_dispatch:
  pull_request:
    paths:
      - 'terraform/**'

jobs:
  terraform-tests:
    uses: canonical/operator-workflows/.github/workflows/terraform_modules_test.yaml@main
    secrets: inherit
    with:
      lxd-controller: true
      terraform-directories: '["terraform/charm", "terraform/product/modules/landscape-scalable"]'

Testing

All mock-provider terraform tests pass:

Success! 16 passed, 0 failed.

This PR was opened by the charmkeeper agent.

[jansdhillon]

Closing in favor of PR #124 which includes all the same changes plus fixes. The branch charmkeeper/terraform is protected by a ruleset requiring PRs, so the fixes could not be pushed directly.