Update terraform module

[Thanhphan1147]

What this PR does

Adds non-breaking outputs/inputs to the Terraform modules to align with CC008 (Charm Terraform Standards). No existing interface changes:

• Charm modules (haproxy, haproxy_spoe_auth, haproxy_ddos_protection_configurator): add the application output exposing the deployed juju_application object.
• Product module: add the models output (model UUID + deployed components) and the metadata output (version), plus a new metadata_version input.
• Tests: assert the new product outputs in terraform/tests/main.tftest.hcl.

All changes are additive — existing app_name, provides, and requires outputs are unchanged.

Why we need it

CC008 mandates an application output for charm modules and models/metadata outputs for product modules. These additions improve module consumability (cross-module wiring, deployment metadata) while remaining backward compatible.

Test plan

• terraform fmt -check -recursive — passes
• terraform validate on all four modules (charm/haproxy, charm/haproxy_spoe_auth, charm/haproxy_ddos_protection_configurator, product) — Success!
• tflint — runs in CI (test_terraform_files.yaml)
• New terraform test assertions for models/metadata run in CI (test_terraform_module.yaml, needs a Juju controller)

Review focus

• terraform/product/outputs.tf — models.components references the new charm application outputs and merges the for_each spoe-auth/oauth applications.
• metadata is intentionally version-only (no timestamps) to avoid plan/apply churn.

Potential breaking changes

None — all changes are additive. Deferred to a future major-bump PR: converting provides/requires to map(object) with kind/name/endpoint (and cross-controller controller field).

Checklist

• I followed the contributing guide
• I added or updated tests as needed (unit and integration)
• If this PR involves Terraform: terraform fmt passes and tflint reports no errors
• I used AI to assist with preparing this PR
• I added or updated the documentation (if applicable) — module READMEs are auto-generated by the terraform-docs workflow
• I updated docs/changelog.md with user-relevant changes
• I added a change artifact / tagged no-release-note