Add `gqlError` serializer

What does this MR do?

Adds gqlError serializer for reporting GraphQL load errors to Sentry with more details.

Screenshots (strongly suggested)

Output formatted like this:

Field 'idm' doesn't exist on type 'Pipeline'.
Locations: line 28 column 7.
Path: query getPipelineDetails, project, pipeline, idm.

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because behind FF.
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Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.

Related to #276949 (closed)