Control plane user assigned identity name

[jamurtag]

The control plane user assigned identity name is set to "uai-${local.cluster_name}".

Either support overriding this, or set to a more descriptive value.

• The default value should probably be "${local.cluster_name}-control-plane" (see docs)
• The opionated module sets all other MIDs to the above format

I'd probably suggest setting to a new default, but provide an option to override, meaning existing users could maintain compatibility.

[dutsmiller]

Included in v4.2.0