Implementation of Cloud Storage function.

[kiliczsh]

Original PR: #72 #71
Configuration keys are missing on the actions machines so that had to handle exceptions.
Google was not allowing me to submit other users commits so that had to copy all, sorry @takuya1981.
@googlebot I consent.

All credits to @takuya1981 .

[hiranya911]

Thanks @kiliczsh for the PR (complete with integration tests). Storage support in .NET has always been a bit of a conundrum. In all other languages of the Admin SDK, we expose the "bucket" as the primary abstraction. For example in Node.js:

const admin = require('firebase-admin');
admin.initializeApp({
  storageBucket: 'example.bucket.name',
});

const bucket = admin.storage().bucket();

But as you already know, in the .NET Storage client, that abstraction does not exist. This results in a very different developer experience. I'd like to run this by our internal API review team, and see what they think about it. Since we have no way of passing a bucket name to the Storage client via Firebase app options, I'm not certain if this integration adds a lot of value.