Global incident rates

Closes https://gitlab.cern.ch/cara/caimira/-/issues/279

This MR links the geographic_cases parameter with the API comming from a WHO database, instead of having a user input, via a server-side API - CasesData. It gets at first the common name for the country in question (via a REST countries API) and then calculates the average value from a WHO database available here.

Added a validation for data that is not up-to-date - if any of the days has a 0 value in the New_cases field (from the database), it means that the dataset is (still) not updated, therefore we don't provide the 7-day rolling average value.

UI Changes:

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