feat: Add settings to exclude content AI bots
Google's Bard and OpenAI's ChatGPT have promised to respect `robots.txt`
instructions with regards to preferences for including website content
in their training data.
This commit adds settings to `_config.yml` to help users choose which
content, if any, they want to request be excluded from the datasets for
these two bots.
The default settings exclude all website content from Bard and ChatGPT,
but keep website content available for search engine crawlers like
Googlebot and Bingbot.
Note that bots are free to ignore the contents of `robots.txt`, so
enabling these settings does not prevent website content from being
included in training datasets.
Learn more: https://www.eff.org/deeplinks/2023/12/no-robotstxt-how-ask-chatgpt-and-google-bard-not-use-your-website-training