Add ability to specify instance type(s), ASG min/max size, and root volume size as variables

[RothAndrew]

Persona

Submitting on behalf of a user who wants to use the example root module we have created with minimal changes in order to do a Big Bang deployment

Description

I'd like to be able to specify which instance type(s) are being used, how many of them will be created, and how big their root volumes are, without having to change terraform code to do it.

Use Case

We want to make it easy for people to use this work via a simple interface (terraform variables)

Impact

If I want to change it I have to change the terraform code, and have an understanding of what the configuration needs to look like.

Completion

The following variables exist, with defaults that are suitable for a reference Big Bang deployment.

In the example root module:

• Variable allowed_instance_types of type list(string) exists, with default value of ["m5a.2xlarge", "m5.2xlarge", "m6i.2xlarge"]
• Variable node_group_min_size of type number with default value of 3
• Variable node_group_max_size of type number with default value of 5
• Variable node_group_desired_size of type number with default value of 3
• Variable root_volume_size of type number with default value of 100

Additionally:

• The E2E tests use smaller values than the defaults to save money (*.large instance type, 2 instances rather than 3, root volume size of 50 instead of 100)

Additional Context

[RothAndrew]

Setting these variables should affect both managed and self-managed nodegroups, to keep things simple and easy to understand.