Embedded structs in models

[skyscrapr]

A number of requests have been made to support embedded structs in models.
#242 has been open for over 3 years.

However I understand this might be a fairly big effort to implement.
Therefore I attempted a minimal change to implement a solution.

See what you think and if appropriate happy to work to get it merged.
Would help me on some other providers that I'm building.

The idea is to allow this type of struct embedding:

type SimpleStruct struct {
	Field1 string `tfsdk:"field1"`
	Field2 int    `tfsdk:"field2"`
	Field3 bool   `tfsdk:"field3"`
}

type ComplexStruct struct {
	SimpleStruct
	Field4 string `tfsdk:"field4"`
}

[hashicorp-cla]

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