Support for TIMESTAMP data type in Configuration Recommendation Engine

When I run the configuration recommendation engine on a schema that contains a field with a TIMESTAMP data type, the following error is thrown:

`{
"_code": 400,
"_error": "java.lang.IllegalArgumentException: Time column can be only INT or LONG: TIMESTAMP"
}`

The [TimeGenerator](https://github.com/apache/pinot/blob/0fe7ef89127b9e920ef369cd9adad9c8b817dde9/pinot-controller/src/main/java/org/apache/pinot/controller/recommender/data/generator/TimeGenerator.java#L68) class doesn’t support a TIMESTAMP data type and hence throws the validation error.

Start with pinot-controller/src/main/java/org/apache/pinot/controller/recommender/data/generator/TimeGenerator.java at the referenced validation near line 68. Trace how the configuration recommendation engine handles schema time columns, then verify that a schema containing TIMESTAMP completes without the reported IllegalArgumentException.

Written by the indexing model from the issue text.