Add security group to a few features

[Elchi3]

Wondering which existing features should belong into the newly created security group for w3c-cg/swag#2. So far we have:

• CSP
• Trusted Types (this PR)

Maybe there is more? @wbamberg, do you want to look through https://web-platform-dx.github.io/web-features-explorer/groups/ to see if anything should be added to the group as well?

[ddbeck]

Approving, but leaving it unmerged for Will's consideration. Feel free to merge when you like.

[wbamberg]

From the list under "Ungrouped features":

• https://web-platform-dx.github.io/web-features-explorer/features/iframe-credentialless/
• https://web-platform-dx.github.io/web-features-explorer/features/permissions/ maybe? It is published by webappsec.
• https://web-platform-dx.github.io/web-features-explorer/features/user-activation/ even more maybe?
• https://web-platform-dx.github.io/web-features-explorer/features/web-cryptography/
• https://web-platform-dx.github.io/web-features-explorer/features/webauthn/ although you already have a group for credentials management and it fits better there
• https://web-platform-dx.github.io/web-features-explorer/features/webauthn-public-key-easy/ although again it fits better in CM

[Elchi3]

Thanks Will, I added the security group to a few more existing features as you suggested. I left out the CM features for now, because, as you say, these might fit better in an "Authentication" group. Features can also be part of several groups. (There are no strict rules around groups yet)