[CDN] Enable CDN for Testnet Beta

[raychu86]

Motivation

This PR adds CDN support for the different networks (MainnetV0, TestnetV0, and CanaryV0).

Currently the CDN is only working for Testnet Beta because only the Testnet Beta blocks have been uploaded to the CDN.

Once mainnet is up and running, blocks can be uploaded to the CDN, and nodes will be able to start fetching blocks from it.

Full CI is being run here.

[vicsn]

Partially resolves: https://github.com/AleoNet/snarkOS/issues/3284

[raychu86]

@vicsn Sorry, had to dismiss your review. I added an additional check to keep the same functionality as before the change.