Add CORS middleware for GQL requests

Description

Add CORS middleware in GQL server

For contributor use:

[ ] Targeted PR against correct branch (see CONTRIBUTING.md)
[ ] Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
[ ] Code follows the module structure standards.
[ ] Wrote unit and integration tests
[ ] Updated relevant documentation (docs/) or specification (x/<module>/spec/)
[ ] Added relevant godoc comments.
[ ] Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
[ ] Re-reviewed Files changed in the Github PR explorer

For admin use:

[ ] Added appropriate labels to PR (ex. WIP, R4R, docs, etc)
[ ] Reviewers assigned
[ ] Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)