feat: make react/react-dom peer dependencies

[saimonmoore]

Description

docz has a direct dependency on react/react-dom which very often conflicts with other dependencies in apps that also have direct dependencies on react/react-dom.

In this PR, we make react & react-dom peer dependencies.

Review

• Check it's all still working.

Pre-merge checklist

• ???

Screenshots

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[draperunner]

But don't you need to remove the direct dependencies? Check core/docz/package.json. It has react and react-dom under both dependencies and peerDependencies. Same goes for docz-theme-default. gatsby-theme-docz has them under dependencies, but no peerDependencies. I'd guess you needed to remove the direct dependencies for these subpackages.

Also, you should update the installation instructions in README.md, adding a mention that react and react-dom has to be installed explicitly.

[saimonmoore]

@draperunner true. Will update.

[pedronauck]

Already merged into feat/gatsby.