[LLRP] Add LLRP Inventory specific service metrics

[lenny-goodell]

🚀 Feature Request

Relevant Package [REQUIRED]

LLRP Inventory

Description [REQUIRED]

Add service metrics relevant to LLRP Inventory. Possibilities:

• Number of inventory moves
• Number of inventory arrivals
• Number of inventory departures

Describe the solution you'd like

Use new Metrics framework to collect these LLRP Inventory service metrics

[lenny-goodell]

closing until we get pull for this from adopters.