Replace deprecated pipenv lock with pipenv requirements

[jeffwidman]

In the versions between what we are currently on in dependaobt-core and the latest versions of pipenv, they deprecated and then completely removed the pipenv lock [-d] command in favor of pipenv requirements [--dev] command.

Since our current version of pipenv supports the pipenv requirements command, let's proactively switch to it now. That will make the future upgrade in #7715 easier.

More context:

• Update docs and add deprecation warning for lock -r pypa/pipenv#5069
• Fix lock -r warning being logged to stdout instead of stderr pypa/pipenv#5091
• Finish removal of the install -r flag for generating requirements.txt pypa/pipenv#5198
• Remove old way of generting requirements. pypa/pipenv#5200

[jeffwidman]

BTW @matteius it was a little painful to track this down.

I'm all for deprecations and even removing functionality, but maybe leave the deprecation message around a little longer?

Our current version is less than two years old and in that time it was deprecated, but then the warning was also removed... would have been nicer if pipenv lock -r became a no-op with a warning message for another 12-18 months so that I didn't struggle trying to figure out if there was a replacement command or if the functionality was completely removed.

The other way this is typically done is with SemVer where I can look at the major version release notes to see the breaking changes. But that wasn't possible since pipenv is using CalVer.

Just a suggestion.

[matteius]

Thanks for the feedback @jeffwidman -- I think that is a reasonable request we can try to accommodate going forward. CC @oz123