chore(flake8): define max docstring length

.flake8

 [flake8]
 max-line-length = 99
+max-doc-length = 99
 docstring-convention=google
 exclude = python, tests/*, __init__.py, src/aura_engine/client/*, meta.py
 ignore = E121,E123,E126,E203,E226,E24,E704,W503,N802,\