[IMP] Added kpis.json store function to BD (kpi and kpi_action)

ddbb scripts/.gitkeep

ddbb scripts/recommender_bayesian.sql

ddbb scripts/recommender_geographic.sql

ddbb scripts/recommender_popularity.sql

ddbb scripts/recommender_preferences.sql

ddbb scripts/recommender_tags.sql

ejemplo.txt

extra_data/kpis.json

extra_data/kpis_area.json

src/app.py

src/constants.py

src/database.py