TINYDOC-3628: Add license_key to the bundling and self-hosted integration examples.

[kemister85]

Ticket: TINYDOC-3628

Site: affected pages on the staging branch (self-hosted variants only; the Cloud pages are unchanged)

Bundling examples:

• Webpack, ES6, npm
• Webpack, ES6, ZIP
• Webpack, CommonJS, npm
• Webpack, CommonJS, ZIP
• Rollup, ES6, npm
• Rollup, ES6, ZIP
• Browserify, CommonJS, npm
• Browserify, CommonJS, ZIP
• Vite, ES6, npm

Integration quick starts:

• Express.js
• Laravel, Composer
• Laravel, ZIP
• Ruby on Rails, ZIP
• Ruby on Rails, tinymce-rails gem
• Django, ZIP
• Bootstrap, ZIP
• Blazor, package manager
• Blazor, ZIP

Changes:

• Added license_key: 'gpl' to the Webpack, Rollup, and Browserify bundling examples.
• Added license_key to the self-hosted Express.js, Laravel, Rails (ZIP and tinymce-rails gem), Django, and Bootstrap quick starts, and LicenseKey to the Blazor ScriptSrc example. Cloud variants are unchanged.
• Added admon-license-key-gpl.adoc, worded without language syntax so it fits the JavaScript, YAML, Python and Razor examples, and included it after every changed example.

Addresses #3436

Pre-checks:

• Branch is correctly prefixed:
• Build passes without console errors, warnings, or issues.

Review:

• Documentation Team Lead has reviewed.