Swap to gigl python environment

[svij-sc]

We are using conda envs w/ names:
gigl and gnn
We should standardize around gigl

GiGL/Makefile

Line 4 in 0297dca

CONDA_ENV_NAME=gnn

GiGL/containers/Dockerfile.builder

Line 44 in 0297dca

RUN conda create -y --override-channels --channel conda-forge --name gigl python=3.9 pip