Add Metrics to the snapshot controller

[xing-yang]

Add Metrics to snapshot controller. Need to be consistent with Metrics in PV/PVC controller.

@jingxu97 to check if Shawn (?) can work on this.

[yuxiangqian]

/assign

[yuxiangqian]

/kind feature

[fejta-bot]

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/lifecycle stale

[xing-yang]

/remove-lifecycle stale

[saad-ali]

Fixed in #227

[saad-ali]

@xing-yang @yuxiangqian You should open one a similar bug on the common snapshot controller

[saad-ali]

Or I guess we can leave this open to track that