Extract client extension

[carlos-schmidt]

• Since automated contract negotiation (client) and AAS management (edc-aas-extension) are not dependent on each other, the client logic will be extracted as a standalone extension.
• This extension will be kept within the EDC-Extension-for-AAS repository.
• In the example folder, both extensions are enabled by default
• Also, cleaned up some code on both the client and the AAS extensions