Add [setup.products] support to fastly compute deploy/publish

[harmony7]

This PR adds first-class support for enabling Fastly Products during the initial fastly compute publish, driven by a new [setup.products] section in fastly.toml.

What this enables

On first publish (service creation only), users can now declaratively enable products such as Fanout, API Discovery, NGWAF, etc., alongside other [setup] resources.

Example:

[setup.products.fanout]
enable = true

[setup.products.ngwaf]
enable = true
workspace_id = "my-workspace"

Key points

New manifest schema

• Adds SetupProducts under [setup]
• Each product has a typed configuration
• NGWAF supports required parameters (workspace_id)
• Validation is product-specific and runs before activation

New setup resource

• Introduces setup.Products, integrated into the existing setup lifecycle
• Runs only when creating a new service (consistent with other [setup] resources)

Clean, table-driven implementation

• Both configuration and activation paths are table-driven
• Adding a new product is a small, localized change
• Avoids reflection; product-specific logic remains explicit and readable

Activation via go-fastly product APIs

• Uses fastly/products/* enable APIs
• Activation happens after service creation
• Spinner output and error handling follow existing CLI patterns

Safe defaults

• Products are enabled only when explicitly configured and enable = true
• Disabled or absent products are ignored
• Manifest round-tripping preserves [setup.products]

Review notes

• Main logic: pkg/commands/compute/setup/products.go
• Manifest changes: pkg/manifest/setup.go
• Deploy flow wires products into the existing setup + creation phases
• Error handling and output are consistent with other setup resources

Why this change

We already support declarative setup for backends, KV stores, secret stores, etc.
Products are a natural extension of that model, and this removes the need for manual post-deploy steps or separate CLI invocations when bootstrapping a new service.

[philippschulte]

LGTM!

I would only suggest adding more tests:

• to trigger a validation failure
• that verifies disabled or omitted products are ignored

But I keep this up to you! Thanks!