Modularity for cosmology metric

[aimalz]

• add a case in make_query(strategy='cosmo', ...) in database.py
• add a placeholder function max_cosmo_info(. . .) in query_strategies.py
• move get_cosmo_posterior.py from ReSSpect demo
• append into metrics.py the metrics of posteriors (calculated along with plotting and shared_metrics.py) in notebooks from ReSSpect metrics