Hide Credentials In Debug Output of `Client`

[mara-schulke]

• Rust Version: rustc 1.55.0-nightly (868c702d0 2021-06-30)
• Runtime version: async-std, will probably apply to all
• OS Version: NixOS 21.11

Steps to Reproduce:

use influxdb::Client;

fn main() {
    println!("{:#?}", Client::new("https://localhost:8086", "db").with_auth("user", "pass"));
}

Results in this output:

Client {
    url: "https://localhost:8086/",
    parameters: {
        "db": "db",
        "u": "user",
        "p": "pass",
    },
    client: Client {},
},

Please think about hiding the username and password from the debug output by implementing debug manually.