Blhc task

A task to represent a build log check using the blhc utility.

The task_data associated to this task can contain the following keys:

input (required): a dictionary describing the input data
- artifact (Single lookup, required): a debian:package-build-log artifact corresponding to the build log to be checked. The file should have a .build suffix.
extra_flags (optional): a list of flags to be passed to the blhc command, such as --bindnow or --pie. If an unsupported flag is passed then the request will fail.

The blhc output will be provided as a new debian:blhc artifact.

The task returns success if `blhc` returns an exit code of 0 or 1, and failure otherwise.

The task computes dynamic metadata as: