Revise GCPBatch infra vs. plugin help menu and defaults

[araghukas]

Relevant PR: #32

Issue

This issue concerns the output of covalent deploy up gcpbatch --help and errors regarding e.g. covalent deploy up gcpbatch --vcpus=12. Note, the latter command fails if --key_path is not specified.

### Recommended Tasks
- [ ] set the `key_path` default to `/Users/<user>/.config/gcloud/application_default_credentials.json"` as in `.tf` files.
- [ ] set `service_account_email` and `project_id` defaults from `gcloud` config (see `gcloud config list`) if possible
- [ ] double check agreement between infra and plugin defaults.

Consider also, changes to Covalent OS:

• distinguish/omit user-settable vs not parameters in/from help table; some param defaults a uniquely auto-generated based on the prefix (see relevant .tf files)