Auto tune table config

Make it easier for people to create a Pinot table which can execute queries in a performant way. Usually this means the Pinot user has to configure things such as inverted indexes. We can do this automatically.

For instance, users can specify something like:

```
"tableIndexConfig": {
“mode”: “auto”
"streamConfigs" : {
"streamType": "kafka",
...
}
}
```

which can be automatically replaced with the necessary config.

The implementation can be done in 2 parts:
1) Have a pluggable interface for defining such customizations
2) Iterate on different types of such auto-tuning implementations.

Start by locating where Pinot parses and applies tableIndexConfig, then review how table configuration and streamConfigs are represented. The issue is complete when a pluggable customization interface is defined and an initial auto-tuning implementation can replace an auto mode with the necessary configuration.

Written by the indexing model from the issue text.