GeoTrellis Documentation Overhaul

[CloudNiner]

This Epic encapsulates the GeoTrellis team effort to overhaul the documentation site replacing RTD with mdoc + docusaurus so that we have CI compiled docs that are built and run on each GeoTrellis commit to master. This work will build on newer docs developed in https://github.com/geotrellis/geotrellis-workshop and https://github.com/geotrellis/geotrellis-docs and is intended to address our goals of updating our out of date documentation and increasing maintainability.

Tasks (Check once broken out into an issue)

• [x] Integrate mdoc / docusaurus build into locationtech/geotrellis + CI
• [ ] Motivation and Installation pages
• [x] Getting Started page
• [x] Rasters and Raster operations
• [x] RasterSources
• [ ] MapAlgebra
• [x] Vector operations (load/unload GeoJSON)
• [x] GDAL
• [ ] Spark

[CloudNiner]

As much as possible, we should align our documentation pages to align with the four quadrants presented in https://documentation.divio.com/

These are:

• Tutorials
• How To
• Reference
• Explanation

I've updated the existing open issues to reflect this as much as possible by aligning on terminology and splitting subtasks in the issue by the quadrant they align with.