Allow OpenSearch style config parameters for data node

## What?
In data node, some OpenSearch parameters are passed through, especially regarding warm tier repositories.
These should allow the dotted OpenSearch-style key to be accepted in addition to the canonical Graylog config key.

This has already been implemented specifically for one use case, but should be extended, at least for the snapshot repository settings
https://github.com/Graylog2/graylog2-server/issues/25116

## Why?
To avoid misconfigurations often seen in community / support issues.

## Your Environment

* Graylog Version: 7.1

Start by tracing the existing implementation for the one OpenSearch-style configuration use case, then identify how data-node configuration handles the warm-tier and snapshot repository settings. Extend the accepted configuration keys to include the dotted OpenSearch forms alongside the canonical Graylog keys, and verify that both forms avoid the reported misconfiguration.

Written by the indexing model from the issue text.