Please don't transform Fn::Sub: to !<!Sub>

[S-Cardenas]

We should be allowed to specify whether we want to output the fully written out version of !<!Sub> or the Fn::Sub version of it. The reason is that the short notation version of this, !Sub, fails when used with Transform::Include. See this example.

[johnbeech]

👍 ( + 1 ) this has really wrecked the readability of our Yaml files... have been trying to dynamically add properties / tags to the document tree, buy yamlDump just creates crazy output that doesn't look good when raising PRs across multiple (20+ repos).

[dsagal]

No objection, but I don't have the bandwidth to work on it. If the underlying js-yaml supports it, I imagine it would be straightforward; if not, then it might not be worth the effort.