buildmaster: Workaround bug #277; fix image locations in docs

* Ensure haikuporter cli is in path until tools.poetry is a little
less melancholy

buildmaster: Bump frontend / backend containers to ghcr

Prepare for release 1.2.8

buildmaster/backend: bump to 1.2.7-9

buildmaster/backend: Capture stderr in report, fix system-packages-dir

* Previous commit added new SYSTEM_PACKAGES_BRANCH var, but didn't
make the same change to the loop script
* Bump to 1.2.7-8

buildmaster: ALlow modifications of system-package set

buildmaster/backend: Bump version for package_repo fixes

* See https://dev.haiku-os.org/ticket/17750 for info

buildmaster: pull hardlink from haiku repo

* The plan was to drop hardlink_packages from the haiku repo, however
users (waddlesplash) are using hardlink_packages locally on their
dev machine for "reasons"
* Instead, wrap the hardlink tool with a wrapper and pull it from
the haiku repo.
* This should all die in a fire and migrate to s3 buckets someday.

buildmaster: Add simplified hardlink_packages tool

* All you need is build-packages in the build-packages
repository, and a repository file from git
* Add better documentation

buildmaster: Split branch spec into two

* SYSTEM_PACKAGE_BRANCH, and BUILD_TARGET_BRANCH
* Master will likely be based on the system-packages of
the last stable release
* Fixes issue trying to use master system_packages

buildmaster: Continue to refactor out un-needed complexity

* Bump containers to 1.2.7-1
* Greatly reduce the "stuff" going on within haikuporter buildmaster
* Yank out generation of system-packages for now
* Ideally we'll automate some extraction from release images / isos
* We can still generate system-packages though via the script in tools
* Simplify some directory structures
* move output to work directory
* move system-packages to work directory

setup.py: Ensure HaikuPorts Builder module is also installed

buildmaster: Rework container to be less complex

* Haikuporter is now packaged with container
* Haiku host-tools now packaged with container
* Reduce the amount of one-off on-disk config files
* Upgrade to Debian bullseye-slim