Add server.conf configuration value for initial Field type refresh interval value

https://github.com/Graylog2/graylog2-server/pull/13018 added system wide index set defaults functionality. As part of this change, it was intended that every index set default configuration setting can also be specified in the `server.conf` file, so that the values properly initialize on the first server startup.

Initially, the `Field type refresh interval` setting was incorrectly mapped to the `index_field_type_periodical_full_refresh_interval` setting which has a different purpose.

This was fixed in https://github.com/Graylog2/graylog2-server/pull/14842. However, the initial value is hard-coded in application code:

https://github.com/Graylog2/graylog2-server/blob/baed4dbb9a7bca47f7bdb75d69812893fa618160/graylog2-server/src/main/java/org/graylog2/indexer/indexset/IndexSetConfig.java#L64

I think we should add a `server.conf` property for this value, so it can be customized for newly initializations of Graylog server clusters (similar to how the other values for shards, replicas etc. can be customized).

There are some existing references to the hard-coded value, so some reworking would need to done.

https://github.com/Graylog2/graylog2-server/blob/baed4dbb9a7bca47f7bdb75d69812893fa618160/graylog2-server/src/main/java/org/graylog2/indexer/indexset/IndexSetConfig.java#L286

If this is done, we should also update the `UPGRADING.md` documentation, which still references the incorrect property:
https://github.com/Graylog2/graylog2-server/blob/a4509254592e29e542e8793bef466f95e12e8d32/UPGRADING.md#new-graylog-cluster-index-set-initialization-defaults See comment (https://github.com/Graylog2/graylog2-server/issues/15320#issuecomment-1520850009) below.
## Context

## Your Environment

* Graylog Version: 5.1.0-SNAPSHOT