chore: change get-data exports

export a function for the specific opensky data, re-org code

src/lib/fetch.mjs

@@ -1,13 +1,9 @@
 import axios from 'axios';
 
-const api = 'https://opensky-network.org/api';
-
 export default axios.create({
-  baseURL: api,
   timeout: 3000,
   responseType: 'json',
   headers: {
-    'X-Custom-Header': 'foobar',
     'Content-Type': 'application/json; charset=utf-8',
   },
 });