Schema merging in build time

[obukhov]

Currently, schemas of services are introspected on service startup and stored in memory which can lead to the situation when different instances (started in different moments of time in case of autoscaling for example) will have different schemas.

To have better consistency and reproducible environment it would be nice to have a way to merge schemas on build time or from files (which can be bundled with the gateway as a part of the docker image).

Please let me know what you think.

[AlecAivazis]

This is another one of those things that have been sitting in the back of my mind for awhile. I think this makes sense for certain teams which means it's probably worth exploring how far we should take it as a library. If you have any ideas on potential APIs, please let me know.