Refactor / Revise how file Paths are handled

While there is some centralization of the file path configurations in the `admin.constants.py` module, code in the script is frequently building new paths from the constants provided in that module. Having the path manipulation code with business logic makes it difficult to read, and understand.

This ticket would create a path library that centralizes the calculation of paths and directories. Instead of code like:

```python
if sat == 'modis':
mosaic = glob(os.path.join(const.INTERMEDIATE_TIF_MODIS, date, 'modis_composite*.tif'))[0]
elif sat == 'viirs':
mosaic = glob(os.path.join(const.OUTPUT_TIF_VIIRS, date.split('.')[0], f'{date}.tif'))[0]
else:
```

Methods would be created to request the paths, example:
```python
mosaic = snow_pathlib.get_intermediate_composite_tifs(sat='modis', date=date)
```

Long term objective is to make the code easier to understand / maintain.