manifest should state prefix is "htn" for hypertension

[comorbidity]

currently incorrect because used covid_symptom as the example.

study_prefix = "covid_symptom"

[sql_config] file_names = [ "observation_vital_signs_bp.sql", "htn_define_dx.sql", "htn_define_rx.sql", "htn_define_bp.sql", ]

[export_config] export_list = [ "htn__count_dx", ]