fix(google-cloud-serverless): Move @types/express to optional peerDeps

[JPeer264]

(closes #18438) (closes JS-1273)

This moves the express types as optional peerDependencies. Since we are only relying on Request and Response and nothing more, this should be a save update. In order to also test against this - I updated the the local types to v5.

The pattern of having the types as optional peerDependencies is already given for our Cloudflare SDK:

https://github.com/getsentry/sentry-javascript/blob/2ef3938fecf872b3d09006538484e5de97123ac5/packages/cloudflare/package.json#L55-L62