[Plugin] Add fpp-ExternalFPP

[github-actions]

Adds fpp-ExternalFPP to pluginList.json, requested in #243.

Plugin repo: https://github.com/jessica12ryan/fpp-ExternalFPP
pluginInfo.json: https://raw.githubusercontent.com/jessica12ryan/fpp-ExternalFPP/refs/heads/main/pluginInfo.json
Category: Monitoring & System Tools
Submitted by: @jessica12ryan
Registered owner (from srcURL): @jessica12ryan (matches submitter)

✅ The automated plugin check passed - no blocking issues found.

Schema, category, and archived/issues-disabled were already checked before this PR existed.

Merging is entirely up to a maintainer's judgement - this PR being open is not an approval, especially if it was opened via /submit over unresolved findings above.

⚠️ Before merging: install this plugin on a real (or test) FPP instance and visually inspect it - the automated check only covers what it can grep for. Confirm the UI actually renders correctly in both light and dark theme, nothing looks broken, and there's nothing the automated findings above wouldn't catch (ads, phone-home, donation links, ...).

A repo maintainer (or @jessica12ryan) can comment /recheck here to re-run the plugin check against the repo's current state and refresh the findings above.