Batch of improvements

[makotom]

• Formatting config.yml. (This is why config.yml has many lines of differences. You will find this diff is better for examining this proposal.)
• Use contexts to pass AWS access keys.
• Respect AWS_DEFAULT_REGION env var. Originally scripts inside this repository was sticking to us-east-1, which is not common especially for JAPAC customers.
• Stop copying AMIs to every region; Since a single customer runs a single instance in a single region, copying to all the region is unnecessary (unlike default Linux AMIs we are providing for machine builds on Server).
• Added an example to set system locale to non-English language (targeting CJK users).
• Setup things with Windows Defender enabled and stop scanning all the files. Based on my research I found out that scanning the entire drive will take longer time than installing things with Windows Defender enabled.
• Synchronizing with the AMI builder for circleci.com
• Documentation enhancements

[makotom]

I'm very interested in this specific piece here:

Setup things with Windows Defender enabled and stop scanning all the files. Based on my research I found out that scanning the entire drive will take longer time than installing things with Windows Defender enabled.

Maybe we should port those changes to Cloud too?

I believe it's worth doing so. Let me confirm this against our AMI builder for .com as well.