feat(deps): declare express types in peer dependencies

[Grmiade]

Summary

Fix #2409

I took the opportunity to also move express in peer dependencies since the project is not always used on top of express.

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[salesforce-cla]

Thanks for the contribution! Before we can merge this, we need @Grmiade to sign the Salesforce Inc. Contributor License Agreement.

[WilliamBergamin]

This looks good to me thanks for working on this 💯

[WilliamBergamin]

You will need to update npm install -> npm install --include=optional in the following files to make the tests pass and update the maintainer experience

• .github/workflows/ci-build.yml
• .github/maintainers_guide.md

Let me know if you would like me to make these changes instead