Diagram - index on accessible sections

As an API consumer, I want to be able to visualise index of observed individuals for transect selection in specific period of time.

Jira ticket: https://ufz-jira.scolution.de/browse/MWB-286

Update: Given formula sum(abundance) / count(sections where accessible = true) is wrong. Use: sum(abundance) / count(sections) where sections are distinct sections from sectionEvents.

AC

• Diagram type ObservationIndex is implemented
• Observation index is calculated by dividing sum of observed individuals with number of accessible sections in the transect selection: sum(abundance) / count(sections), see above
• This diagram shows observation index in the selected time range, according to related transects filter
• displayType: "bar"
• title: "Observation Index"
• xLabel: "Day"
• yLabel: "Index"
• dataSeries JSON format:

[
    {"Day": 1, "Index": 5.24},
    {"Day": 2, "Index": 10.40},
    {"Day": 3, "Index": 20.31},
    {"Day": 4, "Index": 15.13},
    ...
]

• Tests