[YUNIKORN-2886] update Spark operator documentation for YuniKorn integration

[ryankert01]

What is this PR for?

Spark Operator 2.0 has been released with full YuniKorn support. We need to update the website and push this information.

Spark Operator with YuniKorn details:

• Support gang scheduling with Yunikorn
• Set schedulerName to Yunikorn
• Account for spark.executor.pyspark.memory in Yunikorn gang scheduling

See Spark Operator v2.0.0 tag for details.

What type of PR is it?

• [ ] - Bug Fix
• [x] - Improvement
• [ ] - Feature
• [ ] - Documentation
• [ ] - Hot Fix
• [ ] - Refactoring

Todos

• [ ] - Task

What is the Jira issue?

https://issues.apache.org/jira/browse/YUNIKORN-2886

How should this be tested?

Screenshots (if appropriate)

Questions:

• [ ] - The licenses files need update.
• [ ] - There is breaking changes for older versions.
• [ ] - It needs documentation.