Add definition of Group session context and unencrypted session context to SessionHandle

[msandstedt]

Problem

#8441 will introduce amendments to conform to the consensus that has been reached in https://github.com/CHIP-Specifications/connectedhomeip-spec/pull/3588.

This will cover session/exchange matching for secure unicast communication (PASE/CASE). We need to additional code so a SessionHandle can also represent secured group communication and unsecured communication.

Secured group communication is anchored on:

• (today) session key type / encryption type / session ID
• (after likely spec amendments) encryption type / session ID

Unsecured communication is anchored on:

• (today) encryption type / transport context
• (after likely spec amendments) encryption type / implicit unsecured session ID 0 / transport context

Proposed Solution

Add support for these types of session contexts in the SessionHandle object and refactor relevant code paths to use these.