Enable microbatching for document_metadata model

[andrablaj]

What feature do you want to improve?
Starting with v1.9 released in December 2024, dbt-core supports the creation of incremental microbatch models and executing microbatch models in batches.

Enable microbatching for document_metadata model.

Describe the improvement you'd like

@njuguna-n implemented a custom batching improvement for document_metadata in #174 as part of medic/cht-sync#156.

dbt-core's new functionality provides the same capability out of the box.

Additional context

This issue medic/cht-sync#156 contains more context about the testing @njuguna-n and I did of the beta version of this feature.