Placement groups API documentation

[Vernholio]

Added

New endpoints in support of the Placement Groups service launch (Limited Availability):

• Placement Groups List (GET /placement/groups)
• Placement Group View (GET /placement/groups/{groupId})
• Placement Group Create (POST /placement/groups/)
• Placement Group Update (PUT /placement/groups/)
• Placement Group Assign (POST /placement/groups/{id}/assign)
• Placement Group Unassign ([POST /placement/groups/{id}/unassign)
• Placement Group Delete (DELETE /placement/groups/{id})

Changed

Updated endpoints in support of the Placement Groups service launch (Limited Availability):

• Linodes List (GET /linode/instances) - Added placement_group object to show the placement group the Linode belongs to.
• Linode View (GET /linode/instances/{linodeId}) - Added placement_group object to show the placement group the Linode belongs to.
• Linode Create (POST /linode/instances) - Added placement_group parameter to include a new Linode in an existing placement group.
• Linode Clone (POST /linode/instances/{linodeId}/clone) - Added placement_group parameter to include the cloned Linode in an existing placement group.
• DC Migration/Pending Host Migration Initiate (POST /linode/instances/migrate) - Added placement_group parameter to include the migrated Linode in an existing placement group.
• Account View (GET /account) - Includes Placement Group in the capabilities array for accounts with access to the service.
• Region View (GET /regions/{regionId}) - Included various parameters that describe placement group availability and limitations in a region.

Fixed

Minor edits for formatting and compatibility.