fix: Skip zone_awareness_config if zone_awareness is not enabled

[mvalo]

Description

zone_awareness_config should be considered only if zone_awareness is enabled.

Motivation and Context

When zone_awareness_enabled is false and zone_awareness_config is set (whatever the value, even null or {}), the module keeps trying to modify aws opensearch cluster and apply this zone_awareness_config. Obvisouly AWS doesn't consider it since awareness_config is only relevant when awareness is enabled. So this provokes a continuous terraform drift.
Note that we can't just remove the zone_awareness_config from our TF code since we actually uses it for some environements.

How Has This Been Tested?

• I modified the module locally and there is no more a terraform drift. Module won't apply any zone_awareness_config if zone_awareness_enabled is false

[antonbabenko]

This PR is included in version 1.4.1 🎉

[github-actions]

I'm going to lock this pull request because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues. If you have found a problem that seems related to this change, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.