Fix casing in yaml field tags for API resources

[mansam]

The YAML encoder/decoder expects field names to be all-lowercase by default, unlike the JSON encoder/decoder which preserves camelCasing. Because we have strict decoding enabled, this causes failures when camelCased fields are submitted as part of a YAML API request-- the YAML decoder does not recognize them as matching the names of the Go struct's fields. To fix this, we need to explicitly set yaml field tags on the Go structs with the proper casing.