Reset Object state after sending invoking webhook (bug?)

[scrummer]

Current state

As the various clients are being saved as service within the symfony container it becomes absolutely necessary that the services are being reset after the webhook was invoked.
If not, it can cause issues like contents being sent several times when invoking the same client with other content from an other part of the code.

Desired solution

After DiscordWebook::send() was invoked, all the properties (exclusive the ones configured via Symfony configuration) must be reset to the initial state (e.g. clear message, file(s) and remove all embeds from embeds-collection).