CT 1197 graphql schema

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Exposing new schema on tangogql to get metrics:

schema: query { subscribedAttrs { name attribute listeners useEvt eventType } }

Description

Short description of the pull request

Motivation

Background on use case, changes needed

Fixes:

• Items added

Changes:

• changes made

Tests included/Docs Updated?

• Included for each change/fix?
• Passing? (Merge will not be approved unless this is checked)
• Docs updated?
• New packages used/requires npm install?
• Toggle added for new features?