The `nomad volume deregister` command currently returns an error if the volume
has any claims, but in cases where the claims can't be dropped because of
plugin errors, providing a `-force` flag gives the operator an escape hatch.
If the volume has no allocations or if they are all terminal, this flag
deletes the volume from the state store, immediately and implicitly dropping
all claims without further CSI RPCs. Note that this will not also
unmount/detach the volume, which we'll make the responsibility of a separate
`nomad volume detach` command.
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