Support transitions to/from dedicated masters by setting hot tier node_roles to unknown on topology size changes

[tobio]

Description

Adds a plan modifier to ES topology elements, setting the hot tier node_roles to unknown if any topology size changes. This is to support transitioning to/from dedicated masters. It's hard to be more precise here, since we cannot known the eventual node count of a given plan without replicating potentially complicated sizing logic from the API to the provider.

Related Issues

Fixes #601
Related to #635

#635 discusses supporting master tiers without being defined in the TF module. Whilst the effort involved in doing that doesn't seem worthwhile (as above, we'd need to replicate cluster sizing logic into the provider), we may be able to support a zero sized master tier with size ignored on subsequent applies, which then becomes sized by Cloud autoscaling. I'm leaving #635 open to investigate better support there.

Motivation and Context

How Has This Been Tested?

Acceptance test, manually

Types of Changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (improves code quality but has no user-facing effect)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation

Readiness Checklist

• My code follows the code style of this project
• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed