Add the ability for an operator to 'pause' a key

[igalshilman]

Under certain situations it might be useful to pause any further processing of a virtual object's key. Such as a downstream service is experiencing issues, a logic bug that requires a fix, missing credentials, etc'.

[jackkleeman]

Also 'all keys'

[slinkydeveloper]

#3676 somewhat does that already on an invocation basis, that is if an invocation to a given vobj is stuck in a retry loop, it will get paused, thus the vobj will be paused. It won't pause shared handlers though.

Is that enough? shall we close this?