Enhance plugin showcase and submission workflow with updates

[homotechsual]

This pull request introduces several improvements and updates across the plugin submission workflow, documentation, and dependencies. The most significant change is the enforcement of restricted tags in plugin submissions, ensuring only maintainers can apply certain tags. It also upgrades several GitHub Actions and dependencies, clarifies plugin metadata requirements, and adds a new screenshot service configuration.

Plugin submission workflow improvements:

• Enforces that only maintainers can apply restricted tags (favourite, docusaurus) to plugin submissions. If a non-maintainer tries to use these tags, they are removed, and the submitter is notified in a comment. This helps maintain the integrity of highlighted/official listings. [1] [2]
• Updates the actions/github-script version from v8 to v9 for both the plugin PR creation and publish workflows, and updates the actions/checkout version from v6 to v7 in the publish workflow. [1] [2] [3]

Documentation and metadata requirements:

• Clarifies that the source field in plugin metadata is required only for open source plugins; it can be omitted or set to null for closed source plugins.

Configuration and dependency updates:

• Adds a screenshotUrl configuration to use an external service for generating plugin preview images.
• Bumps several development dependencies to their latest patch versions, including @types/node, prettier, and webpack.

[github-actions]

⚡ Successfully deployed to Cloudflare Pages!

• 🔨 Latest commit: b7c3424e237ec21e5fb7a2502248b52bee969a55
• 🔍 Latest deploy log: https://github.com/DocusaurusCommunity/website/actions/runs/29733385262
• 😎 Deploy preview URL: https://head.docusauruscommunitywebsite.pages.dev
• 🌳 Environment: preview

[Copilot]

Pull request overview

This pull request updates the plugin submission and publishing workflows, refreshes a few dev dependencies, and adjusts configuration/docs to support an external screenshot service and clarified plugin metadata expectations.

Changes:

• Enforce restricted plugin tags (favourite, docusaurus) in the plugin submission workflow by stripping them for non-maintainers and notifying the submitter.
• Upgrade workflow actions and dev dependencies (e.g., actions/github-script, @types/node, prettier, webpack) and fix label removal input type.
• Add screenshotUrl configuration for plugin preview generation and clarify source metadata expectations in docs.

Reviewed changes

Copilot reviewed 5 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
yarn.lock	Updates locked versions/checksums for @types/node, prettier, and webpack.
package.json	Bumps dev dependency versions to match the lockfile updates.
docusaurus.config.ts	Adds a screenshotUrl option for the plugin showcase preset.
contributing/plugins.mdx	Clarifies when source is required vs allowed to be null/omitted.
.github/workflows/publish.yml	Updates action versions and corrects removeLabel input type.
.github/workflows/create-plugin-pr.yml	Adds restricted-tag enforcement and improves success comment formatting.

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