Handle the hardcoded configuration values

This patch allows to customize the hardcoded configuration values,
as well as introduce new configuration options for panko services
by configmap template with the specified section:

  panko:
    server:
      configmap:
        DEFAULT:
          api_paste_config: api_paste.ini
        api:
          default_api_return_limit: 100
        storage:
          max_retries: 10

Change-Id: I332862254805b2da479a7e9bf2dde06101045b3a
Related-Prod: PROD-29627
6 files changed