The "User Name" type should map to a "user" risk object and not "other"

[cmcginley-splunk]

• In detection_abstract.py we look for observable of type username
• In practice, the valid type (see SES_OBSERVABLE_TYPE_MAPPING) is User Name; Username/username is invalid and static validation does not allwo for these values
• This is causing a handful of detections to create risk objects of type other instead of type user
• Additionally, device is not a valid observable type per SES_OBSERVABLE_TYPE_MAPPING (used in validation)