Add FIDO U2F security key support to Atlassian Accounts

Summary

Security keys are hardware devices that you can use as your two-step verification. Instead of typing a verification code every time you sign in, you insert the security key and press a button on the device.

Suggestion

This functionality is already available for BitBucket, it would be great if it was made available for Atlassian Accounts as well, since we are on track for 2FA there as well.