Cleanup ecs-migration.yml file (#10278)

This adds the beat name it applies to to each entry. This will allow us to create a migration table for each Beat instead of just having all the fields. It's also potentially relevant for the dashboard migration as a field might be migrated in one beat but not an other.

Further changes:

* Extend all geo.* items to specify each migrated field. This is needed for the dashboard migration
* Extend all user_agent.* items to specify each migrated field. This is needed for the dashboard migration
* Clean up broken entry for resolve.host
* Add Beat name to each entry