[CBM] [Azure] Increase timeout for IMDS credentials request

What's the issue?
We've seen an instance of cbbackupmgr failing to obtain credentials from the managed identity service (using IMDS). As it stands, the timeout for the HTTP request to the local HTTP server (IMDS) is set to one second, in contrast, it looks like AWS uses the config we provide; this means it'll use our HTTP transport.

What's the fix?
We should move away from using the default credential chain, and use one which extends the timeout to be something more reasonable.