apollo-language-server: Include graphql as a peer dependency

**Intended outcome:**

Graphql to be included as a peer dependency in the `apollo-language-server` package, similar to how it's included in the `apollo-graphql` package (https://github.com/apollographql/apollo-tooling/blob/master/packages/apollo-graphql/package.json#L19).

Nice to have: Add support for GraphQL 16.

**Actual outcome:**

Graphql is currently being included as a dependency in the `apollo-language-server` package (https://github.com/apollographql/apollo-tooling/blob/master/packages/apollo-language-server/package.json#L37), and doesn't follow these guidelines: https://leebyron.com/graphql-js-preparing-for-v14/

**Versions**

apollo-language-server: 1.26.9

The package metadata is in packages/apollo-language-server/package.json; compare its graphql entry with packages/apollo-graphql/package.json. Inspect the dependency and peerDependency declarations, then verify the resulting package metadata. Done means graphql is exposed as the intended peer dependency; GraphQL 16 support is an optional follow-up.

Written by the indexing model from the issue text.