Implement influx client extension

[jgrund]

Implement an influx client extenstion that allows for direct
serialization to a struct instead of needing to traverse the result and
build it by hand. Ex:

struct MgsFsTime {
    time: u64,
}

let xs: Vec<MgsFsTime> = client
        .query_into(
            format!(
                r#"
            SELECT mgs_fs,is_mgs_fs
            FROM target
            WHERE mgs_fs='{}' AND is_mgs_fs=true
            ORDER BY time ASC
            LIMIT 2"#,
                fs_names
            )
            .as_str(),
            Some(Precision::Nanoseconds),
        )
        .await?
        .unwrap_or_default();

Signed-off-by: Joe Grund jgrund@whamcloud.io

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