[Backport release-0.4] Fix ecs.Cluster external name configuration

[ulucinar]

(cherry picked from commit 9079649bb43af20a2ecc471abce5616ec364771b)

Description of your changes

I have:

• [X] Read and followed Crossplane's contribution process.
• [X] Run make reviewable test to ensure this PR is ready for review.

How has this code been tested