Add apply_apify_settings to Scrapy subpackage

[vdusek]

Issue

• Related to the Move most of the Scrapy template's logic to Apify SDK #176, but not solving it as a whole.

Description

• This PR moves just a single function from a template to SDK - apply_apify_settings.
• The rest of the suggested changes are related to the logging. I was not able to make them work at first try. So for now let's solve it just for the settings-related helper function, and the rest will be done later.

Testing

• The changes were tested both locally and on the platform.
• Unit tests are ready as well.

[vdusek]

@honzajavorek FYI; also if you would have any feedback on this, I'll be glad. Thanks 🙂.

[honzajavorek]

The implementation looks good, awesome! I've found a few places in the tests where I commented, but they're nothing serious except for the @pytest.mark.only() leftover, which was the decisive factor in why I'm requesting changes.

[janbuchar]

Looks good to me.

[vdusek]

Thank you both guys @honzajavorek, @janbuchar for your opinions. Merging it.

[honzajavorek]

Thanks for shipping it! 🚀