Feat(pyavd): Add _source to AvdBase type

[gmuloc]

Change Summary

Add ._source to AvdBase to get the origin of the different variables at load time of the inputs. It is represented as an InputPath

Component(s) name

pyavd

Proposed changes

cf summary

How to test

pytest + changes in EOS designs

Checklist

User Checklist

• maintain a table per field

Repository Checklist

• My code has been rebased from devel before I start
• I have read the CONTRIBUTING document.
• My change requires a change to the documentation and documentation have been updated accordingly.
• I have updated molecule CI testing accordingly. (check the box if not applicable)

[github-actions]

Review docs on Read the Docs

To test this pull request:

# Create virtual environment for this testing below the current directory
python -m venv test-avd-pr-4838
# Activate the virtual environment
source test-avd-pr-4838/bin/activate
# Install all requirements including PyAVD
pip install "pyavd[ansible] @ git+https://github.com/gmuloc/avd.git@add-path-in-classes#subdirectory=python-avd" --force
# Point Ansible collections path to the Python virtual environment
export ANSIBLE_COLLECTIONS_PATH=$VIRTUAL_ENV/ansible_collections
# Install Ansible collection
ansible-galaxy collection install git+https://github.com/gmuloc/avd.git#/ansible_collections/arista/avd/,add-path-in-classes --force
# Optional: Install AVD examples
cd test-avd-pr-4838
ansible-playbook arista.avd.install_examples