[Feature] Introduce the concept of a global prefix for OpenSearch indexes

The idea is to be able to specify a prefix which is always applied to the index created, and which is controlled by configuration. This is useful for example for installations having their OS cluster administered for them, and they are given a specific prefix they have to respect as security measure.

There was the specifics of `Systems/Monitoring/Databases/MonitoringDB/IndexPrefix` which could do that. That feature was removed in v9.0.

I propose to re-introduce it and generalize it: it could be defined for any OS DB, including `Systems/NoSQLDatabases/IndexPrefix`

The equivalent would be done in `diracx`, though I am not sure yet where to add that piece of configuration

@marianne013 @bertrandrigaud