Monthly SST product availability

[ecologistpablo]

Is your feature request related to a problem? Please describe.
Yes and no. If one wishes to generate monthly averages of products such as SST, chl-a or currents they are currently able to generate dates for all days in a month within a dataframe and then download values for those dates.

Describe the solution you'd like
L3S SST offers a monthly day, night, and DN product on their thredds server (https://mrs-data.csiro.au/imos-srs/sst/ghrsst/L3S-1m/). It would be stupendously glorious if one could access this product quickly and efficently through extractEnv. This would allow users to generate daily L3S SST products, minus that with the monthly average to then produce an anomaly value for any given observation.

This is simple and accessible for current SST products available, however I'm uncertain as to if you will change this product leading into the future (did see an issue request about changing it in near-future) or for products that don't have a monthly average available (ie. GSLA current data).

Thanks!