Implement the "complex mapping key" from YAML spec

[peruzzof]

Please describe your feature request.
Implement the "complex mapping key", per YAML spec (https://yaml.org/spec/1.2.2/ Example 2.11)

Describe the solution you'd like
If we have data1.yml like:
(please keep to around 10 lines )

? - Detroit Tigers
  - Chicago cubs
: - 2001-07-23

And we run a command:

yq '.' data1.yml

it could output

? - Detroit Tigers
  - Chicago cubs
: - 2001-07-23

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
I found this limitation while trying to use a tool called "oasdiff", but the generated YAML is not properly parsed by yq. I raised an issue (Tufin/oasdiff#94) with the tool itself and they pointed me to the specification.

[mikefarah]

As fas as I can tell, this is what yq does already?

yq '.' data1.yaml 
? - Detroit Tigers
  - Chicago cubs
: - 2001-07-23