Add kafka broker public endpoints to module outputs

[MattLamont]

Is your request related to a new offering from AWS?

Is this functionality available in the AWS provider for Terraform? See CHANGELOG.md, too.

• No 🛑: please wait to file a request until the functionality is avaialble in the AWS provider
• Yes ✅: please list the AWS provider version which introduced this functionality

Yes ✅ 4.13.0

Is your request related to a problem? Please describe.

The msk-kafka-cluster module is missing outputs for the public MSK brokers.
The following attributes are available from the AWS provider, but not yet implemented as outputs on the module:

bootstrap_brokers_public_tls
bootstrap_brokers_public_sasl_iam
bootstrap_brokers_public_sasl_scram

https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/msk_cluster#attribute-reference

Describe the solution you'd like.

The attributes listed above for msk clusters be exposed as outputs on this msk-kafka-cluster module.

Describe alternatives you've considered.

N/A

Additional context