Cast Timestamps to RFC3339 strings

[tustvold]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

Currently timestamps are cast to the default chrono format, such as 2018-01-26 18:30:09.453829 +08:00. This is not a defined standard, it appears to be RFC3339 but using spaces.

Describe the solution you'd like

Cast timestamps to strings as RFC3339

Describe alternatives you've considered

We could not do this

Additional context

[waitingkuo]

https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=42768115ab784d65df24ca371c09f985

the debug version follows RFC3339

use chrono; // 0.4.22
use chrono::{TimeZone, FixedOffset};

fn main() {
    let dt = FixedOffset::east(8 * 60 * 60).ymd(2018, 1, 26).and_hms_micro(18, 30, 9, 453_829);
    println!("{}", dt);
    println!("{:?}", dt);
}

2018-01-26 18:30:09.453829 +08:00
2018-01-26T18:30:09.453829+08:00

[waitingkuo]

i think we could use to_rfc3339() while displaying
https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=42768115ab784d65df24ca371c09f985

[jhorstmann]

to_rfc3339_opts also allows specifying how many fractional digits and whether to use a Z instead of +00:00 for UTC.