fix(api-reference): add missing Types and Since in Middleware section

* Add missing Since (see withastro/astro#7578 for
`createContext` and `trySerializeLocals`
* Add missing types (see `packages/astro/src/core/build/types.ts` and
`packages/astro/src/@types/astro.ts`)

src/content/docs/en/reference/api-reference.mdx

@@ -1458,6 +1458,8 @@ Middleware allows you to intercept requests and responses and inject behaviors d
 
 ### `onRequest()`
 
+**Type:** `(context: APIContext, next: MiddlewareNext) => Promise<Response> | Response | Promise<void> | void`
+
 A required exported function from `src/middleware.js` that will be called before rendering every page or API route. It accepts two optional arguments: [context](#contextlocals) and [next()](#next). `onRequest()` must return a `Response`: either directly, or by calling `next()`.
 
 ```js title="src/middleware.js"
@@ -1471,13 +1473,17 @@ export function onRequest (context, next) {
 
 ### `next()`
 
+**Type:** `(rewritePayload?: RewritePayload) => Promise<Response>`
+
 A function that intercepts (reads and modifies) the `Response` of a `Request` or calls the "next" middleware in the chain and returns a `Response`. For example, this function could modify the HTML body of a response.
 
 This is an optional argument of `onRequest()`, and may provide the required `Response` returned by the middleware.
 
 
 ### `sequence()`
 
+**Type:** `(...handlers: MiddlewareHandler[]) => MiddlewareHandler`
+
 A function that accepts middleware functions as arguments, and will execute them in the order in which they are passed. 
 
 ```js title="src/middleware.js"
@@ -1492,12 +1498,20 @@ export const onRequest = sequence(validation, auth, greeting);
 
 ### `createContext()`
 
+<p><Since v="2.8.0" /></p>
+
+**Type:** `(context: CreateContext) => APIContext`
+
 A low-level API to create an [`APIContext`](#endpoint-context)to be passed to an Astro middleware `onRequest()` function.
 
 This function can be used by integrations/adapters to programmatically execute the Astro middleware.
 
 ### `trySerializeLocals()`
 
+<p><Since v="2.8.0" /></p>
+
+**Type:** `(value: unknown) => string`
+
 A low-level API that takes in any value and tries to return a serialized version (a string) of it. If the value cannot be serialized, the function will throw a runtime error.
 
 ## Internationalization (`astro:i18n`)