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:

sentry-javascript/packages/cloudflare/package.json

Lines 55 to 62 in 2ef3938

	"peerDependencies": {
	"@cloudflare/workers-types": "^4.x"
	},
	"peerDependenciesMeta": {
	"@cloudflare/workers-types": {
	"optional": true
	}
	},

[linear]

JS-1273 Bump `@types/express` to v5 for `@sentry/google-cloud-serverless`

[JPeer264]

(moved to draft because I don't want this to be merged yet (see #18438 (comment)), but it can be reviewed)

[github-actions]

node-overhead report 🧳

Note: This is a synthetic benchmark with a minimal express app and does not necessarily reflect the real-world performance impact in an application.

Scenario	Requests/s	% of Baseline	Prev. Requests/s	Change %
GET Baseline	8,599	-	8,696	-1%
GET With Sentry	1,689	20%	1,699	-1%
GET With Sentry (error only)	6,027	70%	6,010	+0%
POST Baseline	1,182	-	1,126	+5%
POST With Sentry	573	48%	580	-1%
POST With Sentry (error only)	1,016	86%	1,050	-3%
MYSQL Baseline	3,254	-	3,339	-3%
MYSQL With Sentry	463	14%	453	+2%
MYSQL With Sentry (error only)	2,642	81%	2,684	-2%

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