Use GCS REST API in place of Firebase Storage REST API.

[taeold]

Description

Firebase Storage REST API has a small issue now where file uploads for payloads >100KB reliably fails for some storage buckets.

Here, we change the implementation of src/gcp/storage.js to call GCS REST API to upload payloads (it doesn't fail for payloads >100KB).

Given that storage.js is placed undergcp/ directory, I think the transition to use GCP API vs Firebase API makes sense.

Scenarios Tested

Try installing an extension (whose total archive size would exceed 100KB) using its local source:

git clone [email protected]:firebase/extensions.git && cd extensions
firebase ext:install ./firestore-counter --project={project-id} --debug

Without the proposed change, the command fails with a 503 from the Firebase Storage API

[debug] [2020-05-29T18:18:17.476Z] >>> HTTP REQUEST POST https://firebasestorage.googleapis.com/v0/b/firebase-ext-eap-uploads/o/firebase-archive-10246n4tFTiaFcPmm.zip  
 <request body omitted>
[debug] [2020-05-29T18:18:19.211Z] <<< HTTP RESPONSE 503 {"x-guploader-uploadid":"AAANsUmdotV4qnjGKD7lViB9G4hQh9im1UXUmvMEpcpEGv2NKw6SEQc-sf_bBrzq1V6FN6RAEmUaeF0MKSE6tl5cLfAmI4XndQ","content-length":"0","date":"Fri, 29 May 2020 18:18:19 GMT","server":"UploadServer","content-type":"text/html; charset=UTF-8","alt-svc":"h3-27=\":443\"; ma=2592000,h3-25=\":443\"; ma=2592000,h3-T050=\":443\"; ma=2592000,h3-Q050=\":443\"; ma=2592000,h3-Q049=\":443\"; ma=2592000,h3-Q048=\":443\"; ma=2592000,h3-Q046=\":443\"; ma=2592000,h3-Q043=\":443\"; ma=2592000,quic=\":443\"; ma=2592000; v=\"46,43\""}

[joehan]

Code looks good to me, just 1 question