Stefan Holderbach f91713b714
Add format duration to replace into duration --convert (#9788)
# Description
Add `format duration` cmd to choose output unit.

This takes the previous `into duration --convert ...` behavior which
returned a string into its own `format duration` command.
This was suprising and not fitting with the general type signature for
the `into ...` commands.

This command for now lives in the `nu-cmd-extra` nursery.

# User-Facing Changes
## Breaking change
Removes formatting behavior from `into duration`
Now use `format duration` instead of `into duration --convert`
## Usage:
```
1sec | format duration us # Output data in microseconds
"2ms" | into duration | format duration sec # go from string to string
```


# Tests + Formatting
Basic example testing (including basic broadcast)
2023-07-30 22:23:36 +02:00
..
2023-07-27 21:32:25 +02:00
2023-07-30 22:16:57 +02:00