chore(workspace): Migrate from yarn to pnpm

[kitten]

Summary

We basically want to achieve a couple things by switching over pnpm.
We get the basic benefits of speed and a nicer setup from pnpm over the aging (old) Yarn.

Its dependencies structure and it enforcing those by default forces us to clean up old discrepancies and implicit, transitive dependencies we collected over time.

This was mainly difficult however to realise because our specific use of tsconfig.json paths for resolving our local packages needed adjustments and specifically needed more changes to Rollup and Vite-based builds. However, this is expected, and we simply "got away" with not having proper resolutions for these before because of the specific symlinking nature of Yarn.

Set of changes

• Add pnpm-workspace.yaml
• Run pnpm import
• Replace resolutions with overrides
• Fix peer dependencies and mismatches
• Update GitHub Actions
• Add missing sub-dependencies to packages
• Update tsconfig.json paths to relative paths
• Update Vite and Vitest to use custom tsconfig-based resolvers plugin
• Update Rollup to use tsconfig-based resolvers plugin
• Update react-static-plugin-md-pages (updated to not use a virtual module)
• Internalise @graphql-typed-document-node/core into @urql/core