chore: Add external contributor to CHANGELOG.md

[javascript-sdk-gitflow]

This PR adds the external contributor to the CHANGELOG.md file, so that they are credited for their contribution. See #20072

[github-actions]

Semver Impact of This PR

🟢 Patch (bug fixes)

📋 Changelog Preview

This is how your changes will appear in the changelog.
Entries from this PR are highlighted with a left border (blockquote style).

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New Features ✨

• (core, node) Portable Express integration by isaacs in #19928
• (deno) Add denoRuntimeMetricsIntegration by chargome in #20023
• (deps) Bump @xmldom/xmldom from 0.8.3 to 0.8.12 by dependabot in #20066

Bug Fixes 🐛

• (cloudflare) Ensure every request instruments functions by JPeer264 in #20044
• (gatsby) Fix errorHandler signature to match bundler-plugin-core API by JPeer264 in #20048

Internal Changes 🔧

Core

• Extract shared endStreamSpan for AI integrations by nicohrubec in #20021
• Remove provider-specific AI span attributes in favor of gen_ai attributes in sentry conventions by nicohrubec in #20011

Other

• Add external contributor to CHANGELOG.md by javascript-sdk-gitflow[bot] in #20073

• Update validate-pr workflow by stephanie-anderson in #20072
• Remove unused tsconfig-template folder by mydea in #20067

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_{🤖 This preview updates automatically when you update the PR.}

[mydea]

steffi does not count as external xD