add cookie support

usage:
 - create cookies.json file somewhere, preferrably outside cobalt directory
 - in docker, you can bind mount it (`volumes` in composefile)
   - if you don't want cobalt to update the cookies, set it to `:ro` (cobalt will print a warning about this, ignore it)
 - set COOKIE_PATH to the absolute path of this file
 - enjoy?

usage in services: probably the simplest api ever
 - import { getCookie, updateCookie } from '../../cookie/manager.js';
 - const cookie = getCookie('<service_name>');
   - add this to headers - `headers: { cookie }`
 - after fetch is done, save potential cookie updates: updateCookie(cookie, fetch.headers)
 - see instagram.js for example usage

.gitignore

@@ -17,3 +17,6 @@ docker-compose.yml
 
 # vscode
 .vscode
+
+# cookie file
+cookies.json