nocar: update deal flow to account for non-car files

[LexLuthr]

Current deal flow:

• The code that creates an index from the file should remain the same: it should return an error because the file cannot be indexed
• The deal execution flow currently pauses at Indexing and shows an error message in the UI
• The deal execution flow does not start to watch the sealing status of the deal

Instead, we should change the deal execution flow such that

• It records that it was not possible to index the deal
• However it still starts to watch the sealing status of the deal

The UI should

• Show the sealing status of the deal
• Flag to the user that the the deal could not be indexed