feat(service-definition): add local filesystem provider

[agustincelentano]

Summary

• Add git_provider = "local" option to the service_definition module that reads specs from the local filesystem using file() instead of HTTP
• New variable local_specs_path points to the directory containing specs/service-spec.json.tpl and specs/links/*.json.tpl
• HTTP data sources are skipped when using local mode (count = 0 / for_each = toset([]))

This enables fast iterative development of service specs without needing to push to a remote repository first.

Usage

module "service_definition_my_service" {
  source = "github.com/nullplatform/tofu-modules//nullplatform/service_definition"

  nrn          = var.nrn
  service_name = "My Service"
  service_path = "services/my-service"

  git_provider     = "local"
  local_specs_path = "${path.root}/../services/my-service"

  available_links = ["connect"]
}

Test plan

• Tested with a real S3 bucket service: tofu init + tofu plan + tofu apply successfully created service_specification and link_specification from local specs
• Verify existing github and gitlab providers still work unchanged
• Verify tofu validate passes with git_provider = "local"