Add Log Messages with SLF4J

[osopardo1]

The current logging processes of qbeast-spark is only covering small cases (such as file filtering in OTreeIndex listFiles operation).

Logs are a very important part of the code, since they help users and developers to understand what is happening, facilitate bug-solving, and help with a better understanding of the code flow. Especially in a framework such as Spark, in which is easy to get lost between the APIs and Catalyst Optimizations.

My proposal is the following:

• Add Logs for Writing Processes. Classes such as SparkDataWriter ,QbeastMetadataOperation and SparkOTreeManager should log information about, at least, the stage they are in.
• Add Logs for Reading. Affecting QuerySpaceBuilder, QueryExecutor and OTreeIndex.
• Add Logs on each PR / code modification. Especially if they contain sensitive processes or they touch some of the critical pieces.

Spark already has a trait for writing such messages, it's called Logging, and this is the description:

/**
 * Utility trait for classes that want to log data. Creates a SLF4J logger for the class and allows
 * logging messages at different levels using methods that only evaluate parameters lazily if the
 * log level is enabled.
 */
trait Logging