0.22.0

• Add new sqlserver relation
• Implement new documentation subsystem
• Change default build to Spark 3.2.1 and Hadoop 3.3.1
• Add new drop target for removing tables
• Speed up project loading by reusing Jackson mapper
• Implement new jdbc metric sink
• Implement schema cache in Executor to speed up documentation and similar tasks
• Add new config variables flowman.execution.mapping.schemaCache and flowman.execution.relation.schemaCache
• Add new config variable flowman.default.target.verifyPolicy to ignore empty tables during VERIFY phase
• Implement initial support for indexes in JDBC relations