Nested inventory data support

[varas]

Description

JSON shape defined for inventory on the public docs:
https://docs.newrelic.com/docs/create-integrations/infrastructure-integrations-sdk/specifications/host-integration-executable-file-json-specifications#inventory

mentions:

inventory data type is a hash of one or more JSON sub-objects

And https://docs.newrelic.com/docs/create-integrations/infrastructure-integrations-sdk/specifications/host-integration-executable-file-json-specifications#inventory

Values may either be a scalar type (string or number) or another hash object of key/values.

But turns out there are some issues:

1. Agent doesn't support several embedded layers: see test failing at Fix: nested inventory items #176

2. Platform ingest all kind of inventory data with success, but later on data is not showned.

3. And there's a UI issue as well:

UI is misleading as nested objects aren't reflected: https://docs.newrelic.com/docs/infrastructure/infrastructure-ui-pages/infra-ui-pages/infrastructure-inventory-page-search-your-entire-infrastructure

The inventory item name is comprised of three elements

And those not even nested keys, they are actually: inventory source split in 2 + 1 single key

Expected Behavior

1. Agent should be able to properly handle nested inventory items.

2. Consider inventory public API docs, so expectations might be made on how clients should behave.

3. Inventory UI might be required to be updated as well to represent nested key/value pair items.

Steps to Reproduce

See above PR failing test. It's payload could be used to reproduce the 3 mentioned issues.

Your Environment

Integration returning nested objects for inventory (test attached payload).

[varas]

1. fixed at Fix: nested inventory items #176
2. this is just raising awareness, not intended to be fixed soon, feel free to create another issue
3. inventory UI is able to display nested items as indexed by the compound key generated by category/source/key1/.../keyN, we might want to update docs to reflect this at https://docs.newrelic.com/docs/infrastructure/infrastructure-ui-pages/infra-ui-pages/infrastructure-inventory-page-search-your-entire-infrastructure