cli: Use WS by default instead of HTTP

[lexnv]

After the substrate patch to remove the RPC HTTP port, trying to fetch the metadata directly from the runtime will fail.

This is because on the HTTP port asking for Metadata_versions will return

Err(Transport(HTTP error: error trying to connect: tcp connect error: Connection refused (os error 111)))

Reproduce

1. Start substrate from the latest master
2. Fetch the unstable metadata via CLI

cargo run --release -p subxt-cli -- metadata  --version unstable --format json

Error:
   0: Other error: The node can only return version 14 metadata but you've asked for something else

Location:
   cli/src/utils.rs:67

However, the Substrate node has access and exposes the V15 under the u32::max.