Add argparser entrypoint & options for download module

[vshlemon]

To enable more flexible usage of the download module provide a command line interface using argparser with the following options:

• Enable user to state which iso-codes to download for (1, many, or all)
• Enable user to state they don't wish to overwrite already downloaded files (overwrite==no)
• Enable user to select the download method they wish to try (httpx, ogr2ogr)
• Enable user to state which path to use for the output to be written to

Provide sensible defaults for the above options, and think about making easily extentible for if we want to use new download source, or upload downloads to a cloud storage location etc.

If necessary update metadata module to make compatible (or perhaps trigger the relevant metadata module calls from the download module call automatically ...?)