Add option to add geospatial metadata to articles to improve discovery

[This feature is motivated by the EarthArXiv preprint server, but I imagine it being useful for other journals as well. I'll stick to preprints in the following for simplicity.]

Is your feature request related to a problem? Please describe.

It can be hard to keep track of new preprints coming out, or to identify work that is relevant to a researcher's work. You can subscribe to feeds or trust social media, but these are also largely based on manual searching and keywords in the title or abstract, which are readily accessible pieces of information. I'm convinced that geospatial metadata could play a great role to help researchers find interesting works. We are working on an OJS plug-in to achieve just that and you can find more in this abstract.

I think this would be a great feature for Janeway too, especially for EarthArXiv or other instances where articles have a clear spatial component.

Describe the solution you'd like

On submission the author is provided the option to enter geospatial metadata. A map is shown where the author can either draw a rectangle (bounding box) or an arbitrary geometry. This geometry is stored in the database.

The same could be done for a "temporal bounding box", so a period of time that the submission is relevant for.

The reader on the website is given the options to

1. see all articles on a map, and by clicking on a geometry, the name and title are shown and the user can click on a link to open the article page
2. can filter search results by providing a time period and/or zoom into a specific area/draw an area of interest on a map

Additional context

I'm happy to contribute code here, though not in the near future, possibly autumn next year. The OJS plug-in under under development beta release of the OJS plugin (https://github.com/TIBHannover/optimetaGeo) might provide some helpful snippets on the UI/mapping side.

I'm sure this is not a simple feature, because to leverage it fully you need a spatial index on the database, which might not be available out of the box, etc.