Improve scripts execution orchestration (#299)

Until now products could declare multiple auto-update methods, but they all had to be of the same kind.
For example if you used the git auto-update method, you could not use an additional github_releases or custom auto-update method.
This is an issue as it prevents us to extend the auto-update process, for example by having a product using the 'git' auto-update method to retrieve all the versions, and a custom script to retrieve support and EOL dates.

This improve the scripts execution orchestration to be able to support auto configurations using a mix of methods, meaning:

- multiple kind of methods, such as git and github_release,
- or multiple custom methods.

A side-effect of those changes is that now a failure in a generic script does not cancel the update of subsequent products.

Another side-effect, unwanted this time, is that now custom scripts managing multiple products, such as apple.py, are now executed multiple times instead of once.

src/apple.py

@@ -51,10 +51,7 @@ VERSION_PATTERNS = {
 
 DATE_PATTERN = re.compile(r"\b\d+\s[A-Za-z]+\s\d+\b")
 
-logging.info("::group::apple")
 soups = [BeautifulSoup(response.text, features="html5lib") for response in http.fetch_urls(URLS)]
-logging.info("::endgroup::")
-
 for product_name in VERSION_PATTERNS:
     with releasedata.ProductData(product_name) as product_data:
         for soup in soups: