add required:"true" tag to struct fields

Author: Benjosh95

templates/go/model_simple.mustache

@@ -636,7 +636,7 @@ type {{classname}} struct {
 {{/isWriteOnly}}
 {{/isReadOnly}}
 {{/required}}
-	{{name}} {{classname}}{{getter}}AttributeType `json:"{{baseName}}{{#required}}{{#isReadOnly}},omitempty{{/isReadOnly}}{{/required}}{{#required}}{{#isWriteOnly}},omitempty{{/isWriteOnly}}{{/required}}{{^required}},omitempty{{/required}}"{{#withXml}} xml:"{{baseName}}{{#isXmlAttribute}},attr{{/isXmlAttribute}}"{{/withXml}}{{#vendorExtensions.x-go-custom-tag}} {{{.}}}{{/vendorExtensions.x-go-custom-tag}}`
+	{{name}} {{classname}}{{getter}}AttributeType `json:"{{baseName}}{{#required}}{{#isReadOnly}},omitempty{{/isReadOnly}}{{/required}}{{#required}}{{#isWriteOnly}},omitempty{{/isWriteOnly}}{{/required}}{{^required}},omitempty{{/required}}"{{#withXml}} xml:"{{baseName}}{{#isXmlAttribute}},attr{{/isXmlAttribute}}"{{/withXml}}{{#required}} required:"true"{{/required}}{{#vendorExtensions.x-go-custom-tag}} {{{.}}}{{/vendorExtensions.x-go-custom-tag}}`
 {{/vars}}
 {{#isAdditionalPropertiesTrue}}
 	AdditionalProperties map[string]interface{}