As a user I would like to configure my cost management plugin

• APIs:
  • https://developers.redhat.com/api-catalog/api/cost-management
  • https://source.redhat.com/groups/public/cost/i/api

• What: add configurable endpoints/credentials for Cost Mgmt APIs; validate on startup.

• Where:

• packages/backend/src/plugins/cost-management/router.ts

• packages/backend/src/plugins/cost-management/service/costManagementClient.ts

• app-config.yaml → costManagement.baseUrl, costManagement.apiToken (or service account)

• Notes: include input sanitization; support separate staging/prod targets.