Add integration test for eksctl utils schema command

[Himangini]

Description

According to the testing spike doc, there are no integration tests for eksctl utils schema command.

Scope

• Validate whether this command's functionality is tested elsewhere in the integration tests or not [collect all the scattered bits in one place if possible?]
• Add integration tests to cover the functionality of this command

Acceptance Criteria

• As a developer
• I should be able to test this command's functionality by running the integration suite.

[Skarlso]

I don't think we need an integration test for

func doSchemaCmd(cmd *cmdutils.Cmd) {
	fmt.Printf("%s", api.SchemaJSON)
}

[Skarlso]

Fine, you know what?! I'm gonna write one anyways. :D