fix: initialize aiohttp client only at startup

[VincentRPS]

Summary

Create's the ClientSession inside of the start function instead of the initializer function.

Checklist

• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
• This PR fixes an issue.
• This PR adds something new (e.g. new method or parameters).
• This PR is a breaking change (e.g. methods or parameters removed/renamed)
• This PR is not a code change (e.g. documentation, README, …)

[EnokiUN]

bro cooks?!