Support architecture groups

[Cyanoxygen]

This allows ACBS to read fields like SRCS__RETRO, PKGDEP__RETRO and BUILDDEP__RETRO without defining the names for every architecture belonging to such group.

[what-the-diff]

PR Summary

• Introduction of a new constant for file path
  Incorporated a new constant, AUTOBUILD_DIR, which will be used as a unified location (/usr/lib/autobuild4/) across our codebase.

• Implementation of simplified architecture-specific variables retrieval
  Added a new function, get_var_arch, in acbs/parser.py which is aimed to optimize the process of extracting variables specific to different system architectures (kinds). This makes the code cleaner and easier to understand.

• Enhancements in dependency handling logic
  Updated the way our system handles dependencies, making them reliant on the new function get_var_arch. This change is intended to increase the maintainability of our code.

• New function for fetching architecture groups
  A new function get_archgroups has been introduced in acbs/utils.py to fetch all defined groups for the host machine, adding to the adaptability of the software.

• Improved data retrieval and error tracking
  The get_archgroups function now reads a JSON file to get group data, leading to more structured and uniform data handling. Alongside, the function features improved exception handling by logging a warning if fetching the group data fails, which ensures the robustness and stability of our system.

[Cyanoxygen]

amd64:

i486: