Top level flag to specify directory to operate in

### Describe the feature or problem you’d like to solve

For example your org has N number of projects you have cloned locally where N may be more then 100. To list all PRs on all projects you need to repeatedly access each project and run `gh pr list` for N times.

Unwanted scenario:
```
cd
gh pr list
cd ..
# Repeat N times
```

### Proposed solution

It would be nice to have such key in to level flags such `--dir`, `--repo` or `--project-path` to have such operation possible:

```
for proj in $(ls); do gh --project-path=$rpoj pr list; done
```
or to have kind of `.ghrc` where someone could list all current projects (configuration file in YAML, JSON, or INI format )

It would be helpful for DevOps teams they usually have to deal with all projects at the same time.