Calculate Air Quality Index for In Situ data

[amehta-scottlogic]

Acceptance Criteria:

Follows https://github.com/ScottLogic/weather-machinists-air-quality-dashboard/issues/31

• Within each document stored in the in_situ_data collection, there is a new property named 'overall_aqi_level'
• The value of this is calculated using the details here: https://ecmwf-projects.github.io/copernicus-training-cams/proc-aq-index.html
• Each pollutant e.g. o3, so2 should also store it's individual AQI value along with the existing value Code from https://github.com/ScottLogic/weather-machinists-air-quality-dashboard/issues/31 should be reused