standarize snapshot functions

[boddumanohar]

rename AUTOSCALER_PVC_SUFFIX to AUTOSCALER_DB_PVC_SUFFIX

Introduce to SnapshotMetadata to hold metadata for snapshot in Kubernetes

class SnapshotMetadata(BaseModel):
    name: str = Field(..., min_length=1)
    namespace: str = Field(..., min_length=1)
    # content_name stays optional because there are runtime scenarios where the
    # VolumeSnapshotContent hasn’t been bound yet
    content_name: str | None

TODO: Write about how this is going to be useful when we add feature for storage API snapshots