enhancement(snapshot): added support for instance restart for snapshots

[ujjwal-ibm]

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Relates OR Closes #0000

Output from acceptance testing:

--- PASS: TestAccIBMISSnapshot_restart (375.70s)
PASS
ok      github.com/IBM-Cloud/terraform-provider-ibm/ibm 380.025s

[astha-jain]

Closes #3153