enrich binding credendials returned inner broker with templated instance credentials (e.g. prometheus endpoint)

[gberche-orange]

• As a service author
• in order to return prometheus endpoint in binding credentials without modifying existing inner broker implementations
• I need coab to enrich returned binding credendials returned inner broker with templated instance credentials (e.g. prometheus endpoint) with a configuration option similar to dashboard url template in paas-templates reproduced below

     # Renders a dashboard url to the url of the dedicated grafana instance.
     # This is using the template using the following parameters
     # {0}: service instance guid
     # {1}: osb-cmdb brokered service instance guid passed as params.x-osb-cmdb.labels.brokered_service_instance_guid or "null" if missing
     # Explanations of grafana URL params:
     # - Selecting 2 days of data so that graphes are not empty by default
     # - autofresh every 15 mins as to not generate unnecessary traffic by default to our servers
     deployment.dashboard-url-template: (( concat "https://grafana-{1}." secrets.cloudfoundry.system_domain "/d/mysql_overview/mysql-overview?orgId=1&refresh=5m&from=now-2d&to=now" ))