Add timeline plot to region view in Explorer

[robbibt]

Currently Explorer provides a very useful timeline feature at the top of Explorer to look at the amount of data that is available through time for an entire product:

It would be very useful if a similar plot could also be added to the region view that appears when a user clicks on a specific tile on the map (e.g. https://explorer.digitalearth.africa/product/ls5_sr/regions/205050). This would allow user to use Explorer to evaluate how much data is available through time for a specific location, rather than the entire product.
This could look something like this:

[pindge]

The default page i.e. https://explorer.digitalearth.africa/product/ls5_sr/regions/205050 should display timeline based on year, drilling down to year, i.e. https://explorer.digitalearth.africa/product/ls5_sr/regions/205050/1986, the display timeline should be based on month, drilling down to the month, the timeline should be shown for days https://explorer.digitalearth.africa/product/ls5_sr/regions/205050/1986/1

[pindge]

To achieve this feature, explorer needs to extend this function

datacube-explorer/cubedash/summary/_summarise.py

Line 54 in 9d6222a

def calculate_summary(

to summarise for each region as well. alternatively, create a variation of calculate_summary to calculate the region summary and sit with

datacube-explorer/cubedash/summary/_stores.py

Line 756 in 9d6222a

if year and month and day:

        if region_code and year:
            return self._summariser.calculate_region_summary(
                product_name,
                year_month_day=(year, month, day),
                product_refresh_time=datetime.now(),
                region_code=region_code,
            )

Explorer would also need to store in cubedash.time_overview per region, snippets blow

                                                                                    timeline_dataset_start_days                                                                                                               
                                                                                                                                                                                                                              
                                                                                                                                                                                                                              
                                                                                                                                                                                                    |                         
                          timeline_dataset_counts                                                   |                                                                              regions                                    
                                          
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
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----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------------------------
----------------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------------------------------
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 {"2017-05-01 00:00:00+00","2017-05-02 00:00:00+00","2017-05-03 00:00:00+00","2017-05-04 00:00:00+00","2017-05-05 00:00:00+00","2017-05-06 00:00:00+00","2017-05-07 00:00:00+00","2017-05-08 00:00:00+00","2017-05-09 00:00:00
+00","2017-05-10 00:00:00+00","2017-05-11 00:00:00+00","2017-05-12 00:00:00+00","2017-05-13 00:00:00+00","2017-05-14 00:00:00+00","2017-05-15 00:00:00+00","2017-05-16 00:00:00+00","2017-05-17 00:00:00+00","2017-05-18 00:00
:00+00","2017-05-19 00:00:00+00","2017-05-20 00:00:00+00","2017-05-21 00:00:00+00","2017-05-22 00:00:00+00","2017-05-23 00:00:00+00","2017-05-24 00:00:00+00","2017-05-25 00:00:00+00","2017-05-26 00:00:00+00","2017-05-27 00
:00:00+00","2017-05-28 00:00:00+00","2017-05-29 00:00:00+00","2017-05-30 00:00:00+00","2017-05-31 00:00:00+00"}                                                                                                               
                                                                                                                                                                                                                              
                                                                                                                                                                                                                              
                                                                                                                                                                                                    | {1,1,1,0,0,0,0,0,0,0,0,0
,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0}                                                             | {103_68,105_74,96_82}