Allow `glab mr checkout` to output status during execution
# Context
When doing a checkout on a MR from `gitlab-org/gitlab`, it takes a couple of seconds (sometimes more) on a top-tier macbook pro.
During this, the command doesn't give any information of what is going on, and it appears as if the command either failed or is stuck.
## Proposal
We should pipe the output from git during `glab mr checkout`, going from:
```bash
$ glab mr checkout <MR_ID>
# ... some seconds of wait
$
```
to
```bash
$ glab mr checkout <MR_ID>
# content below is from executing the git command:
Updating files: 100% (4100/4100), done.
Switched to branch 'branch-name'
$
```
issue