Add New method to TerminalError

[nmvk]

This method helps to throw terminal error from the controller.

Controller code can throw errors like

	if *latestStatus == "create-failed" {
		return nil, ackerr.TerminalError.New(errors.New("cluster cannot be updated as its status is not 'available'."))
	}

Code generator changes - aws-controllers-k8s/code-generator#318

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[RedbackThomson]

I don't quite understand. Is this any different from &TerminalError{err: fmt.Errorf("my error message")}?

[nmvk]

I don't quite understand. Is this any different from &TerminalError{err: fmt.Errorf("my error message")}?

This would throw Unexported field 'err' usage since we want to throw the error outside of the package?

[RedbackThomson]

/lgtm

[ack-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: nmvk, RedbackThomson

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [RedbackThomson]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment