create new bulk host create endpoint

allow system admins, org admins, and inventory admins to bulk create
hosts.

Testing on an "open" licensed awx as system admin, I created 1000 hosts with 6 queries in ~ 0.15 seconds
Testing on an "open" licensed awx as organization admin, I created 1000 hosts with 11 queries in ~ 0.15 seconds

fix org max host check

also only do permission denied if license is a trial

add /api/v2/bulk to list bulk apis available

add api description templates

One motiviation to not take a list of hosts with mixed inventories is to
keep things simple re: RBAC and keeping a constant number of queries.

If there is great clamor for accepting list of hosts to insert into
arbitrary different inventories, we could probably make it happen - we'd
need to pop the inventory off of each of the hosts, run the
HostSerializer validate, then in top level BulkHostCreateSerializer
fetch all the inventories/check permissions/org host limits for those
inventories/etc. But that makes this that much more complicated.

add test for rbac access

test also helped me find a bug in a query, fixed that

add test to assert num queries scales as expected

also move other test to dedicated file

also test with super user like I meant to

record activity stream for the inventory

this records that a certain number of hosts were added by a certain user
we could consider if there is any other additional information we want
to include

awx/api/templates/api/bulk_host_create_view.md

@@ -0,0 +1,16 @@
+# Bulk Host Create
+
+This endpoint allows the client to create multiple hosts and associate them with an inventory. They may do this by providing the inventory ID and a list of json that would normally be provided to create hosts.
+
+Example:
+
+```
+{
+"inventory": 1,
+"hosts": [
+    {"name": "example1.com"},
+    {"name": "example2.com"}
+]
+
+}
+```

awx/api/templates/api/bulk_view.md

@@ -0,0 +1,3 @@
+# Bulk Actions
+
+This endpoint lists available bulk action APIs.