Filtering phase in spark job

[mansu]

Add a filtering phase to spark job to filter spans by service name. Currently, the task is marked as TODO in the code. Opening an issue so we can track it.

This feature is useful in the following ways:

• This filtering can be used to implement a blacklist and whitelist of services that can write spans to this backend.
• Sometimes instrumentation may be buggy or still under development and filtering those spans would be very useful.