Describe the feature or problem you’d like to solve

Here are examples of queries that can be performed using GitHub web tools (here and there):

• is:open is:pr author:OWNER: list all open (pull-requests authored by a given OWNER) on any repository
• is:open is:pr user:OWNER: list all open pull-requests on any (repository owned by a given OWNER)
• is:open is:issue author:OWNER: list all open (issues authored by a given OWNER) on any repository
• is:open is:issue user:OWNER list all open issues on any (repository owned by a given OWNER)

At the moment, unless I am mistaken, all gh commands operate on a single owner-repository at a time, which makes it impossible to answer the above queries.
An example use case for such queries would be to populate a dashboard so that developers that simultaneously work on many repositories can get an overview of the pending PRs and issues that require their particular attention.