Documentation improvements for OpenLineage provider

This PR improves the OpenLineage provider documentation with better organization and expanded content:

• spark.rst: Added separate page for Spark integration, explaining that it's a separate entity from the Airflow provider and requires its own installation and configuration.

• macros.rst: Expanded to be the central documentation for job hierarchy and macros, consolidating information about cross-job dependencies (TriggerDagRunOperator, API triggers, ExternalTaskSensor, Airflow Assets) and how OpenLineage handles job relationships in each scenario.

• troubleshooting.rst: Added troubleshooting page with best practices and common errors, where users trying to debug OL problems can find helpful information.

• supported_classes.rst: Added explanation of what "supported" means, clarifying that all operators emit basic lineage while "supported" operators provide additional operator-specific metadata.

• guides/structure.rst: Added paragraph explaining the difference between the openlineage-python client package and the apache-airflow-providers-openlineage provider package.

• guides/developer.rst: Added section about helper functions e.g. emit_openlineage_events_for_databricks_queries

• provider.yml: Reordered options so that they are alphabetical.

• guides/user.rst: Moved some basic stuff to structure.rst and dev stuff to developer.rst, nothing was left so this file was removed.

Was generative AI tooling used to co-author this PR?

• Yes (please specify the tool below)

Used combination of different models to re-write parts of the docs and look for inconsistencies.

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