Improve CreateOperationContext() in Executor by using sync.Pool

[lkeix]

Describe your PR and link to any relevant issues.

#3362

I have:

• Added tests covering the bug / feature (see testing)
• Updated any relevant documentation (see docs)

[coveralls]

coverage: 59.62% (+0.07%) from 59.549%
when pulling 5091920 on lkeix:master
into aaf44f5 on 99designs:master.

[StevenACoffman]

Hey, I appreciate trying to make performance improvements in gqlgen, but it looks like there's a fair number of test failures with this current code.

[lkeix]

@StevenACoffman
I attempted optimization using sync.Pool, but due to race conditions between WebSocket and POST requests, preventing resource conflicts proved challenging.
Additionally, forcing the use of sync.Pool in this context would lead to an overly complex implementation. Given these issues, I’m planning to close this PR.
Thank you for your time and feedback.