Improve logging for failed migrations

[mshustov]

If migrations v2 failed due to an Elasticsearch response with an empty body (413 error, for example), the log record emitted by SavedObject service won't provide any information about the root cause:

{"ecs":{"version":"1.9.0"},"@timestamp":"2021-07-30T08:17:14.548-04:00","message":"[.kibana] [undefined]: Response Error","log":{"level":"ERROR","logger":"savedobjects-service"},"process":{"pid":45967}}

Run node scripts/jest_integration src/core/server/saved_objects/migrationsv2/integration_tests/migration.test.ts on this branch to reproduce the problem.
We could improve logging by extending the log record with response meta-data: status code, URL. See what we log on the Elasticsearch service level https://github.com/mshustov/kibana/blob/f47c89f52431b56005701bffbae0cfa591413d19/src/core/server/elasticsearch/client/configure_client.ts#L70

[elasticmachine]

Pinging @elastic/kibana-core (Team:Core)