[get_hydrometrie_observations_tr] add an option for handling duplicate entries
code_entity is ambivalent and refers both to
code_station (See https://github.com/BRGM/hubeau/issues/73).
Add an option 'entities' for filtering the API response:
- "station": keep only lines where
code_stationis not null
- "site": keep only lines where
- "both": keep all lines related to stations and sites