Add ability to quiesce node

[krmahadevan]

Closes #2070

This PR provides the following:

1. Expose an end-point on the Hub which lets a user
   quiesce a node. [ Quiesce = don’t route any more new
   session requests to a node and let the in-flight
   sessions run to completion ] via the URL

/lifecycle-manager?action=quiescenode&proxyid=<ProxyId>

2. Add an optional argument to the end-point in (1)
   to also send a recycle signal to the node [ This would
   ensure that the Grid automatically shuts down a
   quiesced node after the in-flight sessions have run
   to completion ] via the URL
   /lifecycle-manager?action=quiescenode&proxyid=<ProxyId>&autoshutdown=true

3. Updated the default hub console to also indicate
   if a particular node is “quiesced” or not.

4. If the user just uses (1) to quiesce a node, then
   they need to shutdown the node on their own. So
   exposed a new URL on the node to support this via
   the URL/lifecycle-manager?action=shutdown

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This change is 

[krmahadevan]

ping @barancev @shs96c - Please help take a look when you get some time.

[krmahadevan]

ping @barancev @shs96c - Please help take a look when you get some time.