The configVersion is a unique identifier for a given version
of the configuration. Each change to the configuration will
update this value. This is typically implemented as a
non-decreasing count or a time-stamp. However, a client should
always treat this as an opaque string.
If specified when updating the resource configuration, the
changes will only be applied if the current configVersion matches the
specified configVersion. This field can be used to guard against
updates that that may have occurred between the time when configVersion
was read and when it is applied.