Describe the bug

When the Camunda Exporter starts up it runs the SchemaManager.startup which will update the mappings of index templates to that defined in the json files of those index templates.

However the json files can also contain a settings block, and currently it will not update the settings block of the existing index template with that of the json file.

This is resulting in such bugs such as the deserialisation issue with type: custom with elasticsearch referenced here elastic/elasticsearch-java#696, which is also causing issues with the camunda migration to 8.8.

To Reproduce

• Create an 8.7 cluster.
• check that operate-list-view template, lowercase normalizer does not have a type custom field
• Create an 8.8 cluster, the operate-list-view template json file for 8.8 has a type custom field so after startup the index template setting should be updated

Expected behavior

The index template settings gets updated with the value from the source json.