Imports a lien that already exists in the public record, so an
organization can track a filing it did not file through Baselayer
alongside the ones it did.

The lien is identified by the state and filing number the filing
office assigned it. An amendment's filing number is accepted too and
resolves to the initial financing statement it amends, because that
is the filing the lien itself is identified by. Only consensual UCC
filings can be imported: statutory, judicial and tax liens are
imposed on a debtor rather than granted by one.

The filing number is matched against the spellings the filing is
known to be ingested under (leading zeros, spacing), so the record
returned carries the public record's canonical filing number, which
may differ from the one posted.

Nothing is filed and nothing is copied: the imported record links to
the public filing, so its status, parties and amendment history are
always the ones the jurisdiction currently reports. Imported filings
cannot be updated, submitted, cancelled or amended — delete the
import to give up the claim.

Importing the same lien twice is not an error: the existing record is
returned with a 200 OK instead of a 201 Created. A lien the
organization already filed through Baselayer is a 409 Conflict
instead — it is the same lien, and a second record would only drift
apart from the first.

Not available to sandbox applications: an import claims a filing
that already exists in the public record, so there is nothing to
simulate.