fix: os.Remove should ignore non existing errors

[jippi]

what

We've seen cases where atlantis unlock fails, and when inspecting the error from logs, we found that it was caused by Atlantis trying to remove a plan file that does not exist.

This change treats the os.NotExists error as a "success" when removing a file (since the outcome is the same, the file should not be there).

We've seen this in production a few times, but most notably when doing ephemeral testing.

why

Removing a file should not fail if the file does not exist.

[jamengual]

LGTM

[jamengual]

@lukemassa any comments? ( since you have been looking at this code recently)

[X-Guardian]

This should at least log a warning within the original functions (not the new utils function), rather than failing silently.

[jippi]

@X-Guardian Happy to add it, but curious why it should log it.

The desired outcome of calling os.Remove() is I want this file not to be there any more which has two happy paths

1. The file exists, and it was successfully removed
2. The file did not exist, which is fine, since I didn't want it to be there anyway

Neither of them is a failure or undesired behavior, and you achieved the desired end state of no file should exist in this path - adding a warning to say I wanted to delete a file, but it wasn't there doesn't (in my opinion) add any value, since its not a problem that the file didn't exist in the first place?

[X-Guardian]

To cover scenario 3, where there is a bug in Atlantis and the filename/path has not been built correctly so that is why the delete failed.

[GenPage]

💯

Straight forward change. Thank you @jippi

[GenPage]

The warning is a good idea. I want to avoid a philosophy of blocking fixes for the sake of perfection. I would like to see a follow-up PR for the warning, as recommended.