In AngularFireFunctions allow for calling `httpsCallableFromURL`

Feature request
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In AngularFireFunctions allow for calling `httpsCallableFromURL` (https://firebase.google.com/docs/reference/js/functions.md#httpscallablefromurl), similar to current call call to `httpsCallable`. With Firebase Cloud Functions V2 this is the only way for calling that new functions (since, they are still in preview mode: https://firebase.google.com/docs/functions/beta/callable#call_the_function).

从 AngularFireFunctions 入口点开始，将其现有的 httpsCallable 支持与 issue 中描述的 Firebase httpsCallableFromURL API 进行比较。当 AngularFireFunctions 能够通过 URL 调用 Cloud Functions V2 端点，并且行为与现有的 callable 支持一致时，即视为完成；如果实现过程识别出相关测试，请添加或更新这些测试。

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