Refactor the Token Metadata Processor into an independent service

[rafaelcr]

Background

Our Stacks API currently exposes a few endpoints that attempt to serve FT metadata. This data is pulled by a background queue that listens to new contracts as they are deployed to the blockchain, but it does not handle token metadata update notifications, NFTs or SFTs. It currently is a complex part of the API that we’re looking to compartmentalize as an external system.

The goal of this issue is to track the process in building a new metadata micro-service, an independent system that manages its own internal logic separately from the API and that can be deployed and scaled separately.

Features

The new Token Metadata Service will support the following token metadata standards:

1. NFTs (SIP-009)
2. FTs (SIP-010)
3. SFTs (SIP-013)
4. Token metadata update notifications (SIP-019: Notifications for Token Metadata Updates stacksgov/sips#72)

NOTE: This service will only process and consume token metadata that follows the guidelines set by SIP-016: stacksgov/sips#44

After processing, all data will be exposed through REST endpoints for external services to consume (endpoint specification TBD).

[saralab]

This has been release in alpha and not yet deployed, closing this.