Make project ID optional in setup script

[corytheboyd-smartsheet]

Checklist

• [ ] All new jobs, commands, executors, parameters have descriptions
• [ ] Examples have been added for any significant new features
• [ ] README has been updated, if necessary

Motivation, issues

When using OIDC to generate a WIF config file, this option makes no sense to require.

Description

Only executes gcloud config set project in setup script if project ID env var is present.

[corytheboyd-smartsheet]

Sorry I don't what your policy is on draft PRs, I just want to leave myself a placeholder to come back to after I clear my plate a bit more.

[KyleTryon]

Closing abandoned. Please let us know if you'd like to continue on this and we can reconvene.