Access to load in memory coastline data

**Description of the desired feature**
I would like to have a method to obtain coastline data in python memory, as dataframe or similar standard format. I think this method fits perfectly within the section `pygmt.datasets` like:

```coast = pygmt.datasets.load_coastline(resolution="keyword", region="ES")```

And the dataframe would look like:

| polygon_id | longitude | latitude | area |
|-------------|-----------|-----------|------|
| 0 | -3.5 | 43.2 | 123|
| 0 | -3.6 | 43.5 | 123|
| 0 | -3.5 | 43.5 | 123|
| 0 | -3.6 | 43.2 | 123|
| 1 | -3.8 | 42.2 | 123|
| 1 | -3.9 | 42.5 | 123|
| 1 | -3.8 | 42.5 | 123|
| 1 | -3.9 | 42.2 | 123|
| 2 | ... | ... | ... |
| ... | ... | ... | ... |

I think this feature is a basic that will be used by many people and can improve the visibility/use of pyGMT. At the end of the day, we want a library to access the basics easily (to plot and also load data)

Also, I miss having direct access to [GEBCO gridded bathymetry data](https://www.gebco.net/data_and_products/gridded_bathymetry_data/) that in coastal/ocean environments is really demanded.

**Are you willing to help implement and maintain this feature?** Yes/No
I would like to help but I am not sure to have the required knowledge... so I think I can't maintain/implement this feature. But let me know... I am always open to learning!

Thank you for your time, have a nice day!