Logging middleware should allow custom

[CermakM]

Inspiration what to put in the description:

I would like to extend the data logged by the logging middleware by custom data. Currently, that's not completely possible. While I can pass custom logging fields to the logger accepted as an input to the middleware, if the data I need comes from other middleware (evaluated from the contextual headers at runtime), then I have no way of injecting them to the logging middelware.

Benefits of the feature

While we can add ad hoc fields to the RequestData, implementing it in a generic way would be more flexible.

Checklist

• I have read the CONTRIBUTING.md.
• I have checked if I'm using the latest version and if I can get the desired behavior by changing the configuration. You might discover that the feature is already available.
• I have searched the existing issues and discussions to see if the feature has already been suggested.