feat: output GRAPHQL_DEBUG message if requested amount is larger than connection limit

[justlevine]

What does this implement/fix? Explain your changes.

This PR adds a debug message to the GraphQL response when the requested amount (first, last) is greater than the graphql_connection_max_query_amount filter value set on the server.

Why

This addition provides developers with an important indication that they're not actually getting the full results requested, which is particularly important to new users coming from traditional WP-PHP for whom setting WP_Query( [ 'posts_per_page' => -1 ] ) is discouraged, but commonplace.

A debug message was chosen over throwing a GraphQLError, both to preserve back-compat, and because IMO this is the ideal GraphQL pattern: a too-large first isnt a schema error, it's something that gets filtered on the backend (ostensibly even based on user role).

More importantly, it keeps the frontend code reusable and server-agnostic. E.g. a pagination pattern uses the last returned item to fetch the next page of results no matter what the server-limit is, whereas if a GraphQLError was thrown, users would need to manually update their frontend code and eschew component libraries / framework starters).

Does this close any currently open issues?

Closes #3012

Any relevant logs, error output, GraphiQL screenshots, etc?

Any other comments?

…

Where has this been tested?

Operating System: Ubuntu 20.04 (wsl2 + devilbox + php 8.1.15)

WordPress Version: 6.4.2

[codeclimate]

Code Climate has analyzed commit 471ca6a and detected 0 issues on this pull request.

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[justlevine]

(relabeled the PR as a feat because of the linter)

[coveralls]

coverage: 84.798% (+0.006%) from 84.792%
when pulling 471ca6a on justlevine:dev/max-query-amount-debug
into 683352d on wp-graphql:develop.