task details should use `YYYY-MM-DDThh:mm:ss±hh:mm` as date time format

[kdheepak]

Feature.

It would be nice if when showing the details of a task using task $n, taskwarrior printed out the date time format including the timezone offset. Currently, this is what it looks like:

My suggestion is that the due row should look like:

Due    2021-11-29T09:00:00+01:00

Use case

Due dates can be in a different "timezone" because of day light savings. It would make it clearer as to what timezone the date corresponds to if this change was made.

For my particular use case, when displaying task details in taskwarrior-tui, users can run into an issue like this:

For reference: https://github.com/kdheepak/taskwarrior-tui/issues/432

cc @Petemir