Move Metrics into airflow_shared library

[amoghrajesh]

Body

https://github.com/apache/airflow/tree/main/airflow-core/src/airflow/metrics

Committer

• I acknowledge that I am a maintainer/committer of the Apache Airflow project.

[KoviAnusha]

Can I work on this item, as no one is assigned yet?

[potiuk]

Sure. But look at other similar work - config and observability are in progress. Those are not really easy tasks mind you :)

[potiuk]

Or actually - I think both metrics and traces are going to eventually end up in #56187, so likely both tasks are covered.

[xBis7]

@potiuk @amoghrajesh Can you assign this to me?