deprecate graphql@15 support

[acao]

after re-enabling the regression tests, we can see that we are no longer compatible with even the last major 15.x version of graphql, so we must remove it from peerDependencies

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🦋 Changeset detected

Latest commit: 0dba52d

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 11 packages

Name	Type
graphql-language-service-server	Minor
@graphiql/plugin-code-exporter	Major
graphql-language-service-cli	Minor
@graphiql/plugin-explorer	Major
graphql-language-service	Minor
codemirror-graphql	Minor
@graphiql/toolkit	Minor
@graphiql/react	Minor
monaco-graphql	Minor
cm6-graphql	Minor
graphiql	Minor

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