poc: [M3-8631] - Use pnpm as our package manager

[bnussman-akamai]

Description 📝

• Uses pnpm as our package manager instead of yarn (classic) 📦
• Doing this because yarn v1 (classic) is no longer maintained 🧶
• Opening this PR to see how chose/far we are from migrating 🆕
• We can't use v9 yet because of pnpm: support v9 lockfile format for dependabot alerts - and/or warn that it is unsupported dependabot/dependabot-core#10534

How to test 🧪

Warning

Work in progress / POC

As an Author I have considered 🤔

• 👀 Doing a self review
• ❔ Our contribution guidelines
• 🤏 Splitting feature into small PRs
• ➕ Adding a changeset
• 🧪 Providing/Improving test coverage
• 🔐 Removing all sensitive information from the code and PR description
• 🚩 Using a feature flag to protect the release
• 👣 Providing comprehensive reproduction steps
• 📑 Providing or updating our documentation
• 🕛 Scheduling a pair reviewing session
• 📱 Providing mobile support
• ♿ Providing accessibility support

[bnussman-akamai]

Will revisit after #11005