Add Iteration Filtering to List Issues

Problem to solve

The GET issues Gitlab API supports filtering issues via their assigned iteration ID. Currently, there is no way to do this via the issue list CLI. It would be useful to be able to filter issues that are in a particular iteration (for instance, issues in the current iteration).

Proposal

An additional parameter be added to the issue list command that allows the user to supply an iteration ID that they're looking for, eg:

# shorthand could be i or whatever desired
glab issue list --assignee=me --iteration 1234

Further details

Adding the ability to filter on iterations would help premium and ultimate customers better use of the CLI to take advantage of some of the features they're paying for.

Links / references