v5.0.0 Apollo Federation v2

• apollo federation v2 is used within schema validation.
  You likely will need to upgrade gateway (see examples folder) and change subgraph schemas. Follow migration guide by apollo.
• apollo composition library migrated from MIT license to ELv2, which adds limitations on how you can use it, which does not affect graphql-schema-registry source code as we only reference it (and its up to you, client, to install and use the library), but docker image is affected as it bundles/distributes the library. Basically you cannot use graphql-schema-registry docker image to commercially compete with Apollo Studio, otherwise its fine to use as internal tool. If you feel this is unfair, feel free to create PR with alternative/pluggable schema validation method.