Clarify supported InfluxDB Versions

[Erik1000]

I find it hard to understand which InfluxDB server versions are actually supported by this crate.
I had some luck using InfluxDB2 but the latest InfluxDB server version is 3, which does not work.
The crate should probably declare somewhere at the top of the README which InfluxDB versions are supported...

[msrd0]

IIRC influxdb 1 and 2 (in compatibility mode) should work and are tested in CI. I've read that influxdb 3 wanted to go back to the influxdb 1 protocol, so it could work, but I have not tested compatibility.

[sheepzh]

I test on v3, there are some compatibility problems I met

Authorization Header

I used influxdb3 create token --admin to create one token, and the output says that the token header is like Authorization: Bearer [token]. But I checked the sourcecode of influxdb-rust, its token header is like

if let Some(ref token) = self.token {
    rb.header("Authorization", format!("Token {}", token))
}

The prefix Token is incorrect for v3.

Ping error

Then I called ping() of client. And the server log shows that influxdb3_server::http: cannot authenticate token e=MissingToken which means it also checks Authorization header for ping requests. While I checked the sourcecode of influxdb-rust again. It doesn't set auth when invoking ping()

pub async fn ping(&self) -> Result<(String, String), Error> {
        let url = &format!("{}/ping", self.url);
        let res = self
            .client
            .get(url)
            .send()      // there is no auth headers set before sending request
            .await
            .map_err(|err| Error::ProtocolError {
                error: format!("{}", err),
            })?;

        // ....
}

[Empty2k12]

These seem like easy fixes.