[V2] Create Helper functions to retrieve client library instances through DIC

[judehung]

For V2 APIs, each services will interact with other services through client libraries as defined in https://github.com/edgexfoundry/go-mod-core-contracts/tree/master/v2/clients, and each services will create their own helper functions to query DIC and get client instances. These helper functions could actually be shared among each services. Per suggestion from edgexfoundry/edgex-go#3061 (comment), we should move these helper functions to go-mod-bootstrap.