Fix/graphql handler errors

[vpintidev]

Description of the Change

This PR introduces a static method AcoreUtils::handle_acore_error() that provides unified error handling for both GraphQL and standard WordPress requests.

Purpose

The goal is to centralize error handling logic across the plugin and ensure consistent behavior depending on the request context:

• GraphQL requests: If GRAPHQL_HTTP_REQUEST is defined and set to true, a UserError exception is thrown, which is properly handled by the GraphQL layer.
• Standard WordPress requests: The user is redirected to the plugin's settings page, and an admin notice is displayed with the provided error message.

Benefits

• Avoids duplicated error-handling logic throughout the codebase.
• Ensures GraphQL clients receive well-structured error responses.
• Provides a better UX for admin users when issues occur in the standard WP context.

Technical Notes

• The GRAPHQL_HTTP_REQUEST constant is defined by WPGraphQL to indicate incoming GraphQL HTTP requests.
• wp_redirect() is followed by exit to stop further execution after redirecting.
• esc_html() is used to ensure safe output in the admin notice.

Potential Improvements

• Consider integrating logging for error tracking and diagnostics.
• Optionally extend support to handle REST API requests with JSON error responses in the future.