feat: add `--mode` to `yarn workspaces focus`

[shnhrrsn]

What's the problem this PR addresses?

Unlike yarn install the current implementation of yarn workspaces focus does not support passing through an InstallMode value.

Closes #3524

How did you fix it?

Copied over the flag + docs from yarn install and passed through to project.install.

Checklist

• [x] I have read the Contributing Guide.

• [x] I have set the packages that need to be released for my changes to be effective.

• [ ] I will check that all automated PR checks pass before the PR gets reviewed.