Enable force refresh by forceRefresh query parameter regardless of refreshRate

[opeco17]

Is your feature request related to a problem? Please describe.
refreshRate is useful to scale Cloud Config clients.
However, we want to make sure that some important clients can get the latest configurations regardless of refreshRate.

Describe the solution you'd like
Allow force refresh regardless of refreshRate by using forceRefresh query parameter.

Describe alternatives you've considered
We can temporarily update refreshRate to 0 while some important clients access Cloud Config
But the new refreshRate is effective for all Cloud Config clients and Config Server might receive huge traffic during that period.
Also updating refreshRate manually every time is tough for operators.

Additional context
PR: #2402

[spencergibb]

Closing in favor of #2402