feat: support optional and conditional integrations (#3590)

* feat(integrations): support optional integrations

By making integration optional, Astro can now ignore null or undefined Integrations instead of giving an internal error most devs can't read/won't understand.

This also enables optional integrations,
e.g.
```ts
integration: [
  // Only run `compress` integration in production environments, etc...
  import.meta.env.production ? compress() : null
]
```

* ci: add tests for optional integration

* docs: add changelog

1 files changed, 1 insertions, 1 deletions

diff --git a/packages/webapi/mod.d.ts b/packages/webapi/mod.d.ts
index a3c49dc5c..b385e82a5 100644
--- a/packages/webapi/mod.d.ts
+++ b/packages/webapi/mod.d.ts
@@ -1,5 +1,5 @@
 export { pathToPosix } from './lib/utils';
-export { AbortController, AbortSignal, alert, atob, Blob, btoa, ByteLengthQueuingStrategy, cancelAnimationFrame, cancelIdleCallback, CanvasRenderingContext2D, CharacterData, clearTimeout, Comment, CountQueuingStrategy, CSSStyleSheet, CustomElementRegistry, CustomEvent, Document, DocumentFragment, DOMException, Element, Event, EventTarget, fetch, File, FormData, Headers, HTMLBodyElement, HTMLCanvasElement, HTMLDivElement, HTMLDocument, HTMLElement, HTMLHeadElement, HTMLHtmlElement, HTMLImageElement, HTMLSpanElement, HTMLStyleElement, HTMLTemplateElement, HTMLUnknownElement, Image, ImageData, IntersectionObserver, MediaQueryList, MutationObserver, Node, NodeFilter, NodeIterator, OffscreenCanvas, ReadableByteStreamController, ReadableStream, ReadableStreamBYOBReader, ReadableStreamBYOBRequest, ReadableStreamDefaultController, ReadableStreamDefaultReader, Request, requestAnimationFrame, requestIdleCallback, ResizeObserver, Response, setTimeout, ShadowRoot, structuredClone, StyleSheet, Text, TransformStream, TreeWalker, URLPattern, Window, WritableStream, WritableStreamDefaultController, WritableStreamDefaultWriter } from './mod.js';
+export { AbortController, AbortSignal, alert, atob, Blob, btoa, ByteLengthQueuingStrategy, cancelAnimationFrame, cancelIdleCallback, CanvasRenderingContext2D, CharacterData, clearTimeout, Comment, CountQueuingStrategy, CSSStyleSheet, CustomElementRegistry, CustomEvent, Document, DocumentFragment, DOMException, Element, Event, EventTarget, fetch, File, FormData, Headers, HTMLBodyElement, HTMLCanvasElement, HTMLDivElement, HTMLDocument, HTMLElement, HTMLHeadElement, HTMLHtmlElement, HTMLImageElement, HTMLSpanElement, HTMLStyleElement, HTMLTemplateElement, HTMLUnknownElement, Image, ImageData, IntersectionObserver, MediaQueryList, MutationObserver, Node, NodeFilter, NodeIterator, OffscreenCanvas, ReadableByteStreamController, ReadableStream, ReadableStreamBYOBReader, ReadableStreamBYOBRequest, ReadableStreamDefaultController, ReadableStreamDefaultReader, Request, requestAnimationFrame, requestIdleCallback, ResizeObserver, Response, setTimeout, ShadowRoot, structuredClone, StyleSheet, Text, TransformStream, TreeWalker, URLPattern, Window, WritableStream, WritableStreamDefaultController, WritableStreamDefaultWriter, } from './mod.js';
 export declare const polyfill: {
     (target: any, options?: PolyfillOptions): any;
     internals(target: any, name: string): any;