doc: Refresh OpenLineage provider docs

[kacpermuda]

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.

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• Read the Pull Request Guidelines for more information. Note: commit author/co-author name and email in commits become permanently public when merged.
• For fundamental code changes, an Airflow Improvement Proposal (AIP) is needed.
• When adding dependency, check compliance with the ASF 3rd Party License Policy.
• For significant user-facing changes create newsfragment: {pr_number}.significant.rst or {issue_number}.significant.rst, in airflow-core/newsfragments.