The context passed to the database layer will auto-close when the HTTP
client disconnects. This will cancel any running query, which is the
expected behaviour. Now this no longer results in an error being logged
in the database layer. Instead, a message is logged at debug level.
The API layer is also adjusted to silence logging of `context.Canceled`
for certain operations, most notably getting all jobs and getting all
tasks of a job. These calls occur when the webapp reconnects after a
restart of the Manager. That may trigger a refresh of the page, which
immediately aborts any pending API calls. This is normal and should not
cause errors to be logged.
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