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
<!-- Include use cases, benefits, and/or goals (contributes to our vision?) -->
### WIP Proposal
Populate defaults for all fields as follows:
1. Cluster Name:
1. ~~Env Scope:~~
1. Project:
1. ~~Zone:~~
1. ~~No of nodes:~~
1. ~~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
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### What does success look like, and how can we measure that?
<!-- Define both the success metrics and acceptance criteria. Note that success metrics indicate the desired business outcomes, while acceptance criteria indicate when the solution is working correctly. If there is no way to measure success, link to an issue that will implement a way to measure this. -->
### Links / references
issue