Rename Index Default initialization server configuration properties

The capability to initialize index set defaults on new Graylog server installations to specific values was introduced in https://github.com/Graylog2/graylog2-server/pull/13018. As discussed in [this comment](https://github.com/Graylog2/graylog2-server/pull/13018#issuecomment-1346454395), we think it would be appropriate to rename/add a prefix to the respective server configuration properties to indicate that they are being used as initialization defaults for the first startup only.

A more general rename of a superset of `elasticsearch_` properties is being discussed [here](https://github.com/Graylog2/graylog2-server/issues/13927). This prefix rename should be coordinated with any general rename, since the config library `fallbackPropertyName` capability only allows us the ability to specify a single fallback property (https://github.com/Graylog2/JadConfig/pull/113).

Full list of index set default initialization properties:
- `elasticsearch_analyzer`
- `elasticsearch_shards`
- `elasticsearch_replicas`
- `disable_index_optimization`
- `index_optimization_max_num_segments`
- `index_field_type_periodical_full_refresh_interval`
- `rotation_strategy`
- `elasticsearch_max_docs_per_index`
- `elasticsearch_max_size_per_index`
- `elasticsearch_max_time_per_index`
- `retention_strategy`
- `elasticsearch_max_number_of_indices`

One potential prefix discussed with @boosty is `index_init_default_`. Another option could be `index_set_init_default_`. Perhaps the `elasticsearch_` portion prefix is not necessary.