[ANCHOR-672] Flatten anchor config fields in value file

[philipliu]

Description

All fields are configurable by the config struct in the value file. Previously, only the callback API was configurable using this method.

Context

We need to be able to configure using a separate Horizon instance. Rather than hardcoding the value mapping like the callback API, this refactors how config management is done.

Testing

• ./gradlew test
• Testing with the demo wallet

Documentation

N/A

Known limitations

This is a breaking change so the deployed environments will need to be updated.

[lijamie98]

Why do we need to keep the empty sep-service.yaml file?