Allow user to specify currency type when configuring field formatter

[drewdaemon]

Describe the feature:
Currency in Kibana is often formatted based on the numeral.js locale which is a global setting:

#135461 added a currency field formatter. We should extend it to allow the user to specify a currency for that particular field.

Describe a specific use case for the feature:
The new metric visualization could use this to display currency values in various formats depending on the type of currency (e.g. a value in EUR and another in USD could both be displayed correctly instead of displaying both as either USD or EUR which is incorrect).

[elasticmachine]

Pinging @elastic/kibana-app-services (Team:AppServicesSv)

[elasticmachine]

Pinging @elastic/kibana-data-discovery (Team:DataDiscovery)

[kertal]

We are closing this issue in order to provide better transparency of priorities. This issue won't be prioritized in the near future. We track it in #163011 for long term planning.