Make dww a co-maintainer for duration_field

Problem/Motivation

https://www.drupal.org/project/datetime_extras now depends on duration_field for a daterange widget I added that defines the end date of the range via an offset, not an absolute value.

There are a growing number of issues with duration_field that would be good to land ASAP and make another official release, including (but not limited to):

#3091695: Remove deprecated code and declare Drupal 9 compatibility
#3093354: Don't use deprecated drupal_process_states() if FormHelper::processStates() exists
#3093358: Enable automated testing for duration_field project
#3020676: Support the #date_increment property in the 'duration' form element.
#3020681: Duration element converting value to an object makes it hard to use for field settings
...

I'd be happy to help out. I'm a careful coder and responsible maintainer. I'd rather put my time into committing these (and other) fixes upstream, instead of continuing to manage patches in all sorts of places (sites where I need this, datetime_extras testing config, etc).

Proposed resolution

Make dww a co-maintainer of duration_field.

Remaining tasks

Agree that this would be a good idea. ;)
Do it.

User interface changes

N/A

API changes

N/A

Data model changes

N/A

Release notes snippet

N/A