feat(openapi): Add modified typescript-fetch template

This template is modified from the original one, to handle multiple
status-code handling of response.

Don't ask me how they work, I don't quite understand them in depth...

openapi-template/modelGenericInterfaces.mustache

@@ -0,0 +1,50 @@
+/**
+ * {{#lambda.indented_star_1}}{{{unescapedDescription}}}{{/lambda.indented_star_1}}
+ * @export
+ * @interface {{classname}}
+ */
+export interface {{classname}} {{#parent}}extends {{{.}}} {{/parent}}{
+{{#additionalPropertiesType}}
+    [key: string]: {{{additionalPropertiesType}}}{{#hasVars}} | any{{/hasVars}};
+{{/additionalPropertiesType}}
+{{#vars}}
+    /**
+     * {{#lambda.indented_star_4}}{{{unescapedDescription}}}{{/lambda.indented_star_4}}
+     * @type {{=<% %>=}}{<%&datatype%>}<%={{ }}=%>
+     * @memberof {{classname}}
+    {{#deprecated}}
+     * @deprecated
+    {{/deprecated}}
+     */
+    {{#isReadOnly}}readonly {{/isReadOnly}}{{name}}{{^required}}?{{/required}}: {{#isEnum}}{{{datatypeWithEnum}}}{{#isNullable}} | null{{/isNullable}}{{/isEnum}}{{^isEnum}}{{{datatype}}}{{#isNullable}} | null{{/isNullable}}{{/isEnum}};
+{{/vars}}
+}{{#hasEnums}}
+
+{{#vars}}
+{{#isEnum}}
+{{#stringEnums}}
+/**
+* @export
+* @enum {string}
+*/
+export enum {{classname}}{{enumName}} {
+{{#allowableValues}}
+    {{#enumVars}}
+    {{{name}}} = {{{value}}}{{^-last}},{{/-last}}
+    {{/enumVars}}
+{{/allowableValues}}
+}
+{{/stringEnums}}{{^stringEnums}}
+/**
+ * @export
+ */
+export const {{classname}}{{enumName}} = {
+{{#allowableValues}}
+    {{#enumVars}}
+    {{{name}}}: {{{value}}}{{^-last}},{{/-last}}
+    {{/enumVars}}
+{{/allowableValues}}
+} as const;
+export type {{classname}}{{enumName}} = typeof {{classname}}{{enumName}}[keyof typeof {{classname}}{{enumName}}];
+{{/stringEnums}}
+{{/isEnum}}{{/vars}}{{/hasEnums}}