Add support for Kubernetes config creation

[daniel-edgedelta]

Summary

This PR adds support for creating Kubernetes configurations through the Terraform provider by including the required environment, fleet_type, and fleet_subtype fields in API requests.

Problem

Previously, attempting to create EdgeDelta configs for Kubernetes environments would fail with:

Error: Could not create the config resource
got non OK http status from: POST /v1/orgs/{org_id}/confs, status: 400, 
response: {"Error":"Failed to validate config create request, err: environment is required"}

Solution

• Added environment, fleet_type, and fleet_subtype fields to the Config struct
• Exposed these as optional Terraform resource parameters with sensible defaults
• Auto-sets fleet_subtype to "Edge" when environment is "Kubernetes" (required by API)
• Extracts the tag from YAML content for proper API request formation

Testing

Tested locally by:

1. Building the provider locally
2. Creating a Kubernetes config successfully
3. Verifying via API that all fields were set correctly

Example Usage

resource "edgedelta_config" "kubernetes" {
  environment    = "Kubernetes"
  fleet_type     = "Edge"
  fleet_subtype  = "Edge"
  config_content = file("config.yaml")
}

Backward Compatibility

Fully backward compatible - all new fields are optional with defaults:

• environment: defaults to "Linux"
• fleet_type: defaults to "Edge"
• fleet_subtype: defaults to empty (auto-set for Kubernetes)