[REQ][Go] Add support for YAML tags to generated model structs

Is your feature request related to a problem? Please describe.

go-yaml relies uses yaml:"" tags from struct definitions to drive marshalling/unmarshalling. When the tags aren't present, it defaults to using field names in all lowercase. This causes problems when sending requests to a server that uses case-sensitive unmarshalling.

Describe the solution you'd like

The go generator already supports a withXml parameter to optionally add xml:"" tags to struct fields. I'd propose adding a withYaml parameter to add yaml:"" tags.

Describe alternatives you've considered

Users can extract model_simple.mustache and add the yaml:"" tags themselves (my current workaround). It's not ideal because the file is large, and there are only 2 lines that need editing to add the tags.

Read model_simple.mustache and the Go generator's existing withXml option first. Add the parallel withYaml option and YAML tags to generated model fields, then verify that generated structs contain the requested tags.