Closes #8550: Implement ASN ranges (#11835)

* Move ASN to a separate module

* Move ASNField from dcim to ipam

* Introduce ASNRange model

* Add relationship from ASN to ASNRange

* Add an available-asns API endpoint

* Add RIR assignment for ASNRange

* Add standard tests

* Move child ASNs to a tabbed view

* Remove FK on ASN to ASNRange

* Add tests for provisioning available ASNs

* Add docs for ASNRange

docs/models/ipam/asn.md

@@ -1,8 +1,8 @@
-# ASN
+# ASNs
 
 An Autonomous System Number (ASN) is a numeric identifier used in the BGP protocol to identify which [autonomous system](https://en.wikipedia.org/wiki/Autonomous_system_%28Internet%29) a particular prefix is originating and transiting through. NetBox support both 32- and 64- ASNs.
 
-ASNs must be globally unique within NetBox, must each may be assigned to multiple [sites](../dcim/site.md).
+ASNs must be globally unique within NetBox, and may be allocated from within a [defined range](./asnrange.md). Each ASN may be assigned to multiple [sites](../dcim/site.md).
 
 ## Fields
 

docs/models/ipam/asnrange.md

@@ -0,0 +1,21 @@
+# ASN Ranges
+
+Ranges can be defined to group [AS numbers](./asn.md) numerically and to facilitate their automatic provisioning. Each range must be assigned to a [RIR](./rir.md).
+
+## Fields
+
+### Name
+
+A unique human-friendly name for the range.
+
+### Slug
+
+A unique URL-friendly identifier. (This value can be used for filtering.)
+
+### RIR
+
+The [Regional Internet Registry](./rir.md) or similar authority responsible for the allocation of AS numbers within this range.
+
+### Start & End
+
+The starting and ending numeric boundaries of the range (inclusive).