Add javascript sdks to monorepo

[jdorn]

Before merge to main:

• javascript sdk
• react sdk
• devmode
• use existing npm package names instead of new ones
• make devmode pull growthbook from context if available
• For sdks, have short README.md files that point to docs.growthbook.io for full docs
• Update docs to reference devmode

After merge to main:

• publish new package version of js sdk
• publish new package version of react sdk
• publish new devmode package to npm
• test packages in production on growthbook website
• push new readmes to old sdk git repos with link to monorepo
• archive old git repos

[vercel]

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app – ./packages/front-end/

🔍 Inspect: https://vercel.com/growthbook/app/73R88DmPg9LePp5dz65Xmak9PHph
✅ Preview: https://app-git-sdks-growthbook.vercel.app

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docs – ./packages/docs

🔍 Inspect: https://vercel.com/growthbook/docs/4X3hVHYpoXvNQ2BHUuvvzYXdwr2e
✅ Preview: https://docs-git-sdks-growthbook.vercel.app

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