feat: mitigate that always have to update irsa s3_object

[soem]

• Fixed:
  • Use the file() with fileexists() to avoid read from the unstable data.local_file source.
    • If file doesn't exist, fallback to the data.local_file source.
• Potential Issues:
  • The s3_object might be incorrect if the keys.json has been changed externally.
    • run apply again might not fix this case, since the null_resource triggers cannot handle this issue,
    • delete the keys.json file might be the only way.
  • The trigger local_cache_exist of null_resource would keep wrong states, and trigger local file updating.
    • from scratch => local_cache_exist: null -> false
    • run again => local_cache_exist: false -> true
    • run again => local_cache_exist: true