automatically fetching the latest checksum

[yibeichan]

as mentioned here ReproNim/reproschema-demo#1
old checksum can't display some UIs properly (e.g., "inputType": "textarea"), so I set up automatic fetching of the latest checksum in GA. it worked well on reproschema-demo

demo-protocol/.github/workflows/build_deploy.yml

Lines 31 to 35 in efe3ff2

	# Fetch the latest commit hash
	- name: Get latest commit hash from reproschema-ui
	run: |
	LATEST_HASH=$(curl -s https://api.github.com/repos/ReproNim/reproschema-ui/commits/master | jq -r '.sha')
	echo "CHECKSUM=$LATEST_HASH" >> $GITHUB_ENV

also, I want to rename the default branch from master to main because main is the default one for all new GitHub repo, so in our demo document, we don't have to add another line to tell them to change master to main when cloning our repo. If no one disagrees, I'll change it