style: relax insert_final_newline rule in .editorconfig to avoid unwanted diffs

[nishant361]

What this PR does

This PR relaxes the insert_final_newline rule in .editorconfig by unsetting it. This helps avoid unnecessary diffs when using editors that automatically insert a final newline, especially in files that previously did not end with one.

Why it's needed

Currently, .editorconfig enforces insert_final_newline = true, but many Lua and other project files don’t follow this rule. Editors that respect .editorconfig add a newline automatically, creating unwanted diffs.

Relaxing this rule and optionally enforcing it using a linter like editorconfig-checker in CI would ensure better consistency and avoid accidental formatting changes during contributions.

Additional context

Related to the discussion started by @spacewander.

Happy to make further adjustments if needed.

Summary

Checklist

• The Pull Request has tests
• A changelog file has been created under changelog/unreleased/kong or skip-changelog label added on PR if changelog is unnecessary. README.md
• There is a user-facing docs PR against https://github.com/Kong/docs.konghq.com - PUT DOCS PR HERE

Issue reference

Fix #[issue number]

[CLAassistant]

All committers have signed the CLA.

[nishant361]

Hi maintainers 👋

I’ve submitted this pull request and just signed the Contributor License Agreement (CLA).
Could you please approve the pending workflows and review the PR when you get a chance?

Thank you! 😊

[StarlightIbuki]

@chronolaw @bungle What do you think

[nishant361]

@StarlightIbuki Hi again 👋

Just a quick follow-up on this PR — I submitted it two days ago and also signed the CLA.
This is my first-ever pull request, so I'm really excited and a bit nervous 😊
Would be grateful if someone could take a look when they get the chance or guide me if I’ve missed anything.

Thank you so much! 😊

[StarlightIbuki]

@spacewander Should we merge this?

[spacewander]

LGTM