v2.2.1

Summary:
Lots of updates to the documentation and added new workable examples to the notebooks. Added DTU23 to JSON database (thanks @robbibt!). Updated the directory to the FES2022 models to the new published urls (thanks @2320sharon!)

Itemized Changes:

• docs: front page with cards and icons (#374)
• fix: updated ftp directory for FES2022 ocean tide model (#376)
• fix: update JSON databases for new FES2022 directory (#376)
• docs: update FES2022 directory in getting started (#376)
• test: retrieve spice kernel file from AWS (#376)
• docs: added example to compare with tide gauges (#377)
• feat: added function for fully-normalized Legendre polynomials (#377)
• test: add ci test for aliasing frequencies (#377)
• refactor: change 1 liner default EPSG to 4326 (#379)
• ci: bump version of upload artifact to v4 (#379)
• docs: start adding more detail for #354 (#381)
• ci: adjust coverage report name for v4 artifact bug (#381)
• docs: expand astronomical argument formalism for #354 (#382)
• docs: add example for plotting tidal potential amplitude spectra (#382)
• docs: split background into separate pages (#382)
• feat: can use np.str_ in doodson numbers (#382)
• docs: add project info (#382)
• docs: add constituent table (#382)
• feat: add DTU23 to providers for #383 (#384)
• fix: missing grid kwarg for reading from TMD3 models (#385)

Full Changelog: 2.2.0...2.2.1