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.

[sfc-gh-tmathew]

Hi @rosspb3,

Thank you for this PR to add Jinja environment configuration options (trim_blocks, lstrip_blocks, etc.).

This PR has been open for about 2 years and likely has significant conflicts with the current codebase. We've also had other Jinja-related changes since then (including PR #353 for data injection).

Questions:

1. Are you still interested in pursuing this feature?
2. If so, would you be able to rebase against the current master branch?

If we don't hear back in the next few weeks, we may close this PR. You're welcome to reopen or create a new PR if you'd like to continue this work later.

Thanks for your contribution!