add: Exactly-once delivery for MM2

[harshini-rangaswamy]

Describe your changes

Added content for exactly-once delivery configuration for Aiven for Kafka MirrorMaker 2.

Preview - https://harshini-mm2-exactly-once-de.aiven-docs.pages.dev/docs/products/kafka/kafka-mirrormaker/howto/exactly-once-delivery

EC-446

Checklist

• The first paragraph of the page is on one line.
• The other lines have a line break at 90 characters.
• I checked the output.
• I applied the style guide.
• My links start with /docs/.

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[nosahama]

Thanks 🙌

[staceysalamon-aiven]

Do we definitely want to include this sample in the Aiven Docs? We have information on the fields in our Terraform documentation, so this would be duplicating info.

This seems like a lot to document for one field. I wouldn't include things like a variables file here since if/how a user does this depends on their setup, internal guidelines, etc. We could instead add this field to the example usage in the TF docs if you think that would be helpful. What do you think?

[harshini-rangaswamy]

Thanks, @staceysalamon-aiven! I agree that the original example was too detailed for a single field, so I’ve simplified it. However, I believe it’s important to include Terraform steps here for the operation, as they provide immediate value to users. A link to the Terraform provider documentation is also included for those who need more detailed information.
cc: @ArthurFlag