If no filepath is provided, do not create a file during sample

[npatki]

Problem Description

As described in issue #1310, the single table sample method has the following functionality:

• If you specify an output_filepath, the sampling function will write to the filepath after every batch, ensuring that you do not lose previously sampled data if there is a crash
• If you do not specify an output_filepath, then the sampling function will still save batched results to .sample.csv.temp (still want to ensure that you have access to some data in the event of a crash). Once the sampling completes, we delete this file.

Problems:

1. When you specify that output_filepath=None, SDV creates a temporary file anyway. This is unintuitive for users who assume that None means that no output filepath will be provided. It is also unintuitive that SDV deletes the file after-the-fact.
2. In the event of a crash, there is a message asking users to check .sample.csv.temp, which is unexpected. This was meant to give the user some data rather than nothing. But practice there are always 0 rows in this file, because the default batch_size is kept equal to the sample size.
3. There is no way to turn off the functionality for saving to a file. Users in both Crashes on FileNotFoundError for .sample.csv.temp #1310 and Sampling should not create a file called ‘.sample.csv.temp’ by default #2029 mention that they'd like to turn it off because it does not work well within their filesystem (they are not worried about crashes during sampling).

Expected behavior

• If the output_filepath=None, we should no longer create or write to a temporary file. This will align with the user expectations and it will enable more forms of usage. In the event of a crash, update the error message. There will no longer be a file to reference.
• If output_filepath is provided, we should create and periodically write to the file as we do today. In the event of a crash, the error message should continue to ask the user to check the file.

Default: We can make the default None. In the future, we should figure out a better default for batch_size for very large samples. In such a case, it would make sense to have a output filepath supplied as a default.