Function sync_datastores

Syncs all buckets from `ds_from` to `ds_to` with `-synced` appended to the ID of the destination bucket. is_push: a bool indicating if we're pushing local buckets to the sync dir (as opposed to pulling from remotes) src_did: source device ID

(
    ds_from: &dyn AccessMethod,
    ds_to: &dyn AccessMethod,
    is_push: bool,
    src_did: Option<&str>,
    sync_spec: &SyncSpec,
)