[demo] API side changes to allow running jobs against multiple inventories

[AlanCoding]

SUMMARY

Allows running a job template against multiple inventories. Still need:

• a related runner patch is necessary for this to run - Fix bugs in streaming code you hit if using more than 1 inventory ansible-runner#1166
• RBAC, creating one of this inventory type constitutes a delegation of "use_role" of source inventories
• UI updates to make this work
• some API work for back-links of stuff
  • show multi-inventory jobs in historical jobs for a constituent inventory
  • show a host list for the "multiple" kind of inventory combining the source inventories
  • some minor adjustments of related links and stuff

This is offered as an option to solve #371 and #1999, since users can simply use host patterns in their playbooks to target the hosts they want.

This is also a counter-point to more complex solutions to #371 that still involve loading the full host set, per discussions with @nitzmahone @sivel and others. If a solution results in Ansible core loading all of the source inventory hosts, then it would appear inferior to this (simple) solution in every way I can think of. This multi-inventory approach is a good fallback if we're not able to implement the other proposals, but I also hope that it helps to cull obvious design dead-ends before we waste too much time on them.

This example runs on an execution node, where "alan" and "steve" are hosts from two separate inventories.

ISSUE TYPE

• New or Enhanced Feature

COMPONENT NAME

• API

[AlanCoding]

closing to put up another version with a more complete PoC