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/cgit.py

@@ -1,9 +1,9 @@
-from common import dates, endoflife, http, releasedata
+from common import dates, http, releasedata
 
 """Fetches versions from repositories managed with cgit, such as the Linux kernel repository.
 Ideally we would want to use the git repository directly, but cgit-managed repositories don't support partial clone."""
 
-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 + '/refs/tags')