feat: add yamlfmt for YAML

[alexeagle]

Fixes #152

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Type of change

• New feature or functionality (change which adds functionality)

For changes visible to end-users

• Relevant documentation has been updated

Test plan

• New test cases added

[f0rmiga]

Thanks for adding this. It's great to have the ability to configure the YAML style.

[alexeagle]

Sure - @f0rmiga note that I didn't do any testing here about the tool locating config files, but as we're bazel running with PWD in the source directory I'd expect it to work.