Rendered Markdown preserves meaningless whitespace of original message

[ldrozdz]

The formatting of the original MML/PML message gets serialized as MD whitespace. This is incorrect as indentation should be meaningless.

Repro: change the formatting of payloads/templated_message_all_tags.messageml or payloads/expanded_single_jira_ticket.presentationml and observe unit test failures. The tests should be insensitive to formatting.