Refactor scripts arguments handling (#456)

- remove the use of environment variables to get directory paths,
- make use of arguments / argparse instead of environment variables in `update.py` and `report.py`,
- automatically guess the data directory in `latest.py` based on the script's location,
- propagate log level to auto scripts,
- move `list_configs_from_argv` from `endoflife` module to `releasedata` module,
- use `list_products` in `latest.py` to load the product's frontmatters.

src/unity.py

@@ -1,4 +1,4 @@
-from common import dates, endoflife, http, releasedata
+from common import dates, http, releasedata
 
 """Fetches the Unity LTS releases from the Unity website. Non-LTS releases are not listed there, so this automation
 is only partial.
@@ -16,7 +16,7 @@ Note that it was assumed that:
 
 The script will need to be updated if someday those conditions are not met."""
 
-for config in endoflife.list_configs_from_argv():
+for config in releasedata.list_configs_from_argv():
     with releasedata.ProductData(config.product) as product_data:
         html = http.fetch_html(config.url)