9654 device weight (#10448)

* 9654 add weight fields to devices

* 9654 changes from code review

* 9654 change _abs_weight to grams

* Resolve migrations conflict

* 9654 code-review changes

* 9654 total weight on devices

* Misc cleanup

Co-authored-by: Jeremy Stretch <jstretch@ns1.com>

docs/models/dcim/devicetype.md

@@ -41,6 +41,10 @@ Indicates whether this is a parent type (capable of housing child devices), a ch
 
 The default direction in which airflow circulates within the device chassis. This may be configured differently for instantiated devices (e.g. because of different fan modules).
 
+### Weight
+
+The numeric weight of the device, including a unit designation (e.g. 10 kilograms or 20 pounds).
+
 ### Front & Rear Images
 
 Users can upload illustrations of the device's front and rear panels. If present, these will be used to render the device in [rack](./rack.md) elevation diagrams.

docs/models/dcim/moduletype.md

@@ -35,3 +35,7 @@ The model number assigned to this module type by its manufacturer. Must be uniqu
 ### Part Number
 
 An alternative part number to uniquely identify the module type.
+
+### Weight
+
+The numeric weight of the module, including a unit designation (e.g. 3 kilograms or 1 pound).

docs/models/dcim/rack.md

@@ -65,6 +65,10 @@ The height of the rack, measured in units.
 
 The external width and depth of the rack can be tracked to aid in floorplan calculations. These measurements must be designated in either millimeters or inches.
 
+### Weight
+
+The numeric weight of the rack, including a unit designation (e.g. 10 kilograms or 20 pounds).
+
 ### Descending Units
 
 If selected, the rack's elevation will display unit 1 at the top of the rack. (Most racks use asceneding numbering, with unit 1 assigned to the bottommost position.)