Enable custom plausible link

[surchs]

For external deployments that might want GDPR compliant usage statistics (e.g. the BIC node) we should allow a way to define things like the plausible script to be added at runtime (i.e. after the image is built).

Similar to how we add ours in

query-tool/.github/workflows/deploy.yaml

Lines 32 to 36 in 9bd09fc

	- name: Add prod scripts
	run: |
	add_script='<script async src="https://w.appzi.io/w.js?token=YVTHd"></script><script defer data-domain="query.neurobagel.org" src="https://plausible.neurobagel.org/js/script.js"></script>'
	# Need to use single quotes around sed to avoid ! to be interpreted as a history expansion character
	sed -i 's|<!-- Additional script tags -->|'"${add_script}"'|' index.html