When installing a model, the previous, graceful logic would increment a
suffix on the destination path until found a free path for the model.
But because model file installation and record creation are not in a
transaction, we could end up moving the file successfully and fail to
create the record:
- User attempts to install an already-installed model
- Attempt to move the downloaded model from download tempdir to
destination path
- The path already exists
- Add `_1` or similar to the path until we find a path that is free
- Move the model
- Create the model record
- FK constraint violation bc we already have a model w/ that name, but
the model file has already been moved into the invokeai dir.
Closes#8416
c5069557f3