Document GitHub serverside limit on URL length

[gukoff]

What article on docs.github.com is affected?

https://docs.github.com/en/github/managing-your-work-on-github/about-automation-for-issues-and-pull-requests-with-query-parameters

What part(s) of the article would you like to see updated?

Document the serverside limit of 8191 bytes URL.

Additional information

[welcome]

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