Create URL generator for HEAL

[gaurav]

Should be set up to be used in the same way the URL generator for dbGaP and NIDA are set up:

dug/src/dug/utils.py

Lines 32 to 35 in 8e8de2d

	def get_dbgap_study_link(study_id):
	base_url = "https://www.ncbi.nlm.nih.gov/projects/gap/cgi-bin/study.cgi"
	return f'{base_url}?study_id={study_id}'