Support plugin configurations within config.properties

[tdcmeehan]

Hello folks,

Wanted to get any inputs on supporting configuring plugins directly within config.properties.

Firstly, why do this at all? When configuring multiple plugins, it can be a bit of a pain to see the at a glance configuration of Presto, because they're scattered across several properties. I think it would be easier to provide a default instance of a configuration if we allow inline plugin configuration in the main config file.

The idea would be to add a special prefix for plugins, such as plugin., then followed by a key indicating the plugin itself (such as hive), then a key indicating the instance of the plugin if applicable (such as hive_interactive1). There's a bit of disorganization in how we configure plugins, and I think this would clean it up a bit. Keys which are not prefixed by plugin. will continue to be strictly validated, and to prevent an accident where a core property is added which has this prefix, we can add a checkstyle rule which would fail the build if it's added at any point in the future.

We could still support the old way of configuring plugins. I have a couple ideas

1. Preferred. We could fallback to the old way if no property of the matching plugin and plugin instance are found. Perhaps we can throw if both are present simultaneously.
2. We could treat the plugin properties in config.properties as a default, and override when a dedicated etc config present.

Appreciate any thoughts.