Sensor model and reference system documentation

[AustinSanders]

Likely needs some restructuring, but not sure what the best split is. Maybe split the ecosystem stuff off from the sensor models doc, leaving us with 1. reference systems / reference frames 2. Sensor models + the CSM 3. Software ecosystem (3a USGS ecosystem, 3b extended ecosystem)

Licensing

This project is mostly composed of free and unencumbered software released into the public domain, and we are unlikely to accept contributions that are not also released into the public domain. Somewhere near the top of each file should have these words:

This work is free and unencumbered software released into the public domain. In jurisdictions that recognize copyright laws, the author or authors of this software dedicate any and all copyright interest in the software to the public domain.

• [x] I dedicate any and all copyright interest in this software to the public domain. I make this dedication for the benefit of the public at large and to the detriment of my heirs and successors. I intend this dedication to be an overt act of relinquishment in perpetuity of all present and future rights to this software under copyright law.

[AustinSanders]

For convenience of review, mermaid sequence diagram renders to:

[jlaura]

Instead of ISIS Data / PDS Data, would you consider 'intrinsics (e.g., SPICE instrument kernel)' and 'extrinsics (e.g., SPICE ephemeris)' or something like that? My thinking is that the source really does not matter, it's the content that is important.

[jlaura]

@AustinSanders Apologies, I had a change request in, but you made a ton of changes and it looks good. I think any additional changes can/should happen incrementally after publication.

The link check CI failure looks like a red-herring because of how the @TODO is structured.

[jlaura]

@AustinSanders Any chance the new glossary additions can go in in another PR? Happy to review. This is a big add to this PR that appeared super close to being mergable.