URI lookups should support HTTP

### Description

A URI field that does not support HTTP is kind of like a car that does not go on roads. It should be supported or documented.

Ref: https://druid.apache.org/docs/latest/development/extensions-core/lookups-cached-global.html

### Motivation


Start with the cached global lookup documentation linked in the issue and trace the URI-field configuration and its HTTP handling. Determine whether the expected outcome is HTTP support or documentation of the limitation; done means the chosen behavior is implemented or clearly documented and verified against the lookup configuration.

Written by the indexing model from the issue text.