Use a sensible default for DuckDB when the environment does not set $HOME

[ferruzzi]

DuckDB defaults to using $HOME for files, but serverless environments don't always set that. When that value is not available, we'll use a default.

Specifically noticed this when the DuckDB system, tests failed on Lambda Executor, but should apply to other serverless environments and maybe some other non-standard installations that don't set $HOME. If $HOME isn't set, then fall back on a temp file.

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[vincbeck]

One test is failing

[o-nikolas]

I'd actually argue this is the responsibility of the admin to configure these environments with a HOME directory. I had planned to configure that as part of our CDK configuration for the Lambda executor, but it must have gotten dropped in the flurry of CRs I put together

[ferruzzi]

I actually looked into this a little more based on the CI failure and I think my solution only works on Duck 1.5.0+, which is another argument against this fix; we'd at least have to gate it behind a version check AND still add the requirements to the docs (and fix the CDK for the system test runner on the AWS side) either way. Before 1.5 the home_directory wasn't accepted as a config-time config option (hence the CI failure) and there is a bug report on 1.3.2 saying it didn't actually work back then.

So this fix would/could only work in 1.5.0+, we'd either need a more robust fix (like using SET home_directory='...' after connecting, maybe? untested, but I think that's the next thing I would try) or use this fix behind a version check and bump minver.

But based on Niko's comment, I'll close this PR and put up a new one this afternoon which just adds some docs and makes it explicit that this is an environment requirement. We can revisit if we want to add this later, gate it behind a proper Duck version check, etc, but the docs should be updated either way and would be universal instead of only fixing latest.