Use type-only imports for axios

TypeScript type checker complains about imported types in clients generated for axios backend

Type-only imports: https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-8.html#type-only-imports-and-export

(cherry picked from commit 4867366)

Author: vrslev

src/templates/core/axios/request.hbs

@@ -1,6 +1,6 @@
 {{>header}}
 
-import axios, { AxiosError, AxiosRequestConfig, AxiosResponse } from 'axios';
+import axios, { AxiosError, type AxiosRequestConfig, type AxiosResponse } from 'axios';
 import FormData from 'form-data';
 
 import { ApiError } from './ApiError';