Add support for Jinja environment options in schemachange configuration.

[rosspb3]

Added ability to configure some Jinja Environment settings within the schemachange configuration via a new "jinja" section. This section would allow users to customize several parsing and rendering options in Jinja like trim_blocks lstrip_blocks, block_start_string, block_end_string, variable_start_string, variable_end_string, but disallows changing settings which could impact the behavior of schemachange like undefined, loader, enable_async.