feat: Support merging Object attributes

[bbckr]

Currently the library only supports merging hcl Blocks and nested Blocks recursively. When it comes to attributes (in setAttrs), this is all or nothing, which means both objects and arrays are replaced entirely w/o attempting to merge.

Attributes are represented as a list of hcl Tokens, so in order to merge attributes, we need to be able to parse the list of Tokens to make sense of the type of value we are dealing with.

Acceptance criteria:

• Be able to recursively merge nested objects
• Any MR should have this (or a similar) test case added to hcl_test.go:

	tests := []struct {
		name    string
		input   input
		want    string
		wantErr error
	}{
		{
			name: "merge nested duplicate",
			input: input{
				a: `module "b" {

	c = {
		"foo" = {
			value = 1
		},
	}
}
			`,
				b: `module "b" {

	c = {
		"bar" = {
			value = 2
		},
	}
}
			`,
			},
			want: `module "b" {

	c = {
		"foo" = {
			value = 1
		},
		"bar" = {
			value = 2
		},
	}
}
`,
		},
	}