Plugin e2e: support node 24 and drop support for node 18

[jackw]

What this PR does / why we need it:

LTS day is almost upon us. This PR updates plugin-e2e's engines to drop support for node 18 and include support for node 24.

Marking it as a major breaking change given we're dropping support for node 18, which is end of life.

Which issue(s) this PR fixes:

Fixes #2107

Special notes for your reviewer:

📦 Published PR as canary version: Canary Versions

✨ Test out this PR locally via:

npm install [email protected]
npm install @grafana/[email protected]
# or 
yarn add [email protected]
yarn add @grafana/[email protected]

[Copilot]

Pull Request Overview

This PR updates the Node.js version requirements for the plugin-e2e package to align with current LTS support, dropping Node 18 (which has reached end of life) and adding support for Node 24.

Key Changes:

• Updated the engines.node field to require Node 20 or higher (up to Node 24)

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[github-actions]

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[github-actions]

Playwright test results

Image Name	Version	Result	Report
grafana-dev	12.3.0-18773734011	✅
grafana-enterprise	12.2.1	✅
grafana-enterprise	11.5.10	✅
grafana-enterprise	10.3.12	✅
grafana-enterprise	9.3.16	✅
grafana-enterprise	8.5.27	✅

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