Allow flag to automatically set HF_HUB_OFFLINE=1 and OFFLINE=True environment variables during tira execution

[mam10eks]

Previously, submissions that used HF transformers had to manually set HF_HUB_OFFLINE respectively OFFLINE environment variables so that the code runs in the TIRA sandbox (i.e., no internet connection). Still, it is very easy to forget this, hence, the goal of this ticket would be to automatically set those environment variables.