Performance: Move Practitioner signatures into Minio

[jpye-finch]

hearth-dev.Practitioner.extensions[url='http://opencrvs.org/specs/extension/employee-signature'] still has user's base64 embedded signature in it.

Change every place where Practitioner is written to first upload the image to MinIO and only then write the URL into the collection. For existing record, implement a migration to do the same. There should exist migrations where we've done the same previously.