Adding functions and scripts for downloading, extracting, and processing observations, initial conditions, land cover types, ERA5 drivers for anchor sites within NA.

[DongchenZ]

Description

This PR includes:

1. script for preparing required data sets (ERA5; AGB, LAI, SMAP, and SOC; land cover) for anchor sites.
2. script for preparing initial conditions (AGB, LAI, Soil moisture, SOC) for anchor sites.
3. updated function for searching ecoregion within NA.
4. functions for downloading and extracting soil moisture from the CDS server.
5. function for downloading and extracting MODIS land cover products.
6. function for extracting AGB initial condition from the GeoTIFF files.
7. function for extracting ISCN SOC from existing Rdata file.

   Motivation and Context

Review Time Estimate

• [ ] Immediately
• [ ] Within one week
• [x] When possible

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [ ] My change requires a change to the documentation.
• [ ] My name is in the list of CITATION.cff
• [ ] I have updated the CHANGELOG.md.
• [ ] I have updated the documentation accordingly.
• [ ] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.

[infotroph]

As currently structured this PR adds more than 100 megabytes of data files to the package, which is far outside the norm for R package size -- CRAN wants special justification for anything with more than 5 MB of data or more then 10 MB for the whole package. Do the shapefiles and Rdata files really need to be distributed as part of data.land or can they be stored elsewhere and read in as needed?