🔤 Libplanet.Explorer GraphQL schema checks in CI

[riemannulus]

Context

We do not have any checks about Libplanet.Explorer GraphQL schema. And this prevented us from properly responding to schema changes or proactively noticing unintended ones.

So, we need the CI checker for GraphQL schema.

Rationale

The Ci should be run following tasks.:

• Build schema.graphql from Libplanet.Explorer
• Check it is compatible with the previous schema.
  • If not, it can be merge when approved by one of the @planetarium/libplanet teams.

Ref

https://www.apollographql.com/tutorials/voyage-part3/06-schema-checks-in-ci