Stop a Linear fetch

Administrators only. Poll this while an import runs: the counts move as rows are written. `errors` holds the first 100 rows that could not be written (in row order) and `errorCount` the true total. An import in another workspace is a 404. `errors` also holds the rows the plan left out, which the worker saves when it starts (the upload is deleted when the job ends, so this is the only record of which rows and why). Notes, such as a value that was dropped from an issue that was still imported, are not rows left out and are not kept. At most 500 are saved, and when the plan had more, a last entry with code `more_problems` says how many are not listed. `errors=all` returns up to 10,000 instead of 100, for downloading them. `pendingPeople` lists the people the file named as assignee who were not members of the workspace, most issues first, with how many of this import's issues are still waiting for each. Those issues were created unassigned and are handed to the person when they are added to the workspace, so a person who has since joined is no longer listed. It is empty until the import has ended, and at most 50 are listed. `pendingPeopleTotal` and `pendingIssuesTotal` count everyone and every issue still waiting, however many are listed.