New APIs:
* protocomm_open_session()
* protocomm_close_session()
This allows external applications using protocomm to manually create and close sessions.
These internally call the new_transport_session() and close_transport_session() APIs implemented by the security scheme in use.
Updated unit tests with usage of new APIs
* This manages secure sessions and provides framework for multiple transports.
* The application can use protocomm layer directly to have application specific extensions for provisioning (or non-provisioning) use cases.
* Following features are available for provisioning :
* Security - Security0 (no security), Security1 (curve25519 key exchange + AES-CTR encryption)
* Proof-of-possession support for Security1
* Protocomm requires specific protocol buffer modules for compilation which can be generated from the `.proto` files in the `proto` directory using make.
Co-Authored-By: Amey Inamdar <amey@espressif.com>
Co-Authored-By: Anurag Kar <anurag.kar@espressif.com>
