chore: handle (pre)import canceled status in the import handler and importer
Second part of #527 (closed) where we initialize a ticker to check every 1s
if the repository has been manually canceled by checking the migration_status
column. This column is updated by calling the DELETE import endpoint.
If it the status is canceled, we simply call the cancel
context function inside the import go routine.
Builds on top of !935 (merged)
Related to #527 (closed)
Edited by Jaime Martinez