Populate default values for all fields in GKE cluster creation form

Problem to solve

The GKE creation form requires user to enter too many values before being able to create. This elevates the barrier for entry.

Further details

WIP Proposal

Populate defaults for all fields as follows:

1. Cluster Name:
2. Env Scope:
3. Project:
4. Zone:
5. No of nodes:
6. Machine Type:

Note: RBAC field is going away in https://gitlab.com/gitlab-org/gitlab-ce/issues/55902 so not considering for this issue

Documentation

What does success look like, and how can we measure that?

Links / references