docs: add user manual for Management API

[arnoweiss]

WHAT

Currently, the "docs/kit" folder contains outdated docs. However, documentation on using the tractusx-edc service is sparse. Thus, there should be a management

WHY

Documenation on how to integrate the tractusx-edc service via the Management API is outdated but required by application developers who want to expose their APIs to the dataspace.

HOW

Rename docs/kit section to docs/manual and add updated management API walkthrough that currently lives here and is set to be updated. Content from the PR to the deployed Connector-Kit may provide initial content for the rework.

FURTHER NOTES

There was a discussion in the matrix-channel about this as well. Having the Management-API-Walkthrough here was suggested by @ndr-brt.

Please be sure to take a look at
our contribution guidelines and
our PR etiquette.