Make a glossary of terms used in dst project

Several terms like "[OffChain ID](https://github.com/direct-state-transfer/dst-go/blob/5cf83f46971aaa17ba8243bcaf7a6dea5922a4ef/identity/manager.go#L33)", "[OnChain ID](https://github.com/direct-state-transfer/dst-go/blob/5cf83f46971aaa17ba8243bcaf7a6dea5922a4ef/identity/manager.go#L34)", "[Session ID](https://github.com/direct-state-transfer/dst-go/blob/5cf83f46971aaa17ba8243bcaf7a6dea5922a4ef/channel/offchain_primitives.go#L35)", "[Sender Role](https://github.com/direct-state-transfer/dst-go/blob/5cf83f46971aaa17ba8243bcaf7a6dea5922a4ef/channel/manager.go#L37)", "[Receiver Role](https://github.com/direct-state-transfer/dst-go/blob/5cf83f46971aaa17ba8243bcaf7a6dea5922a4ef/channel/manager.go#L41)" etc., are used in the code base of direct state transfer project and also referenced in the documentation.

A glossary can be created to consolidate such project specific terms and their meanings / interpretations.

Start with the linked definitions in identity/manager.go, channel/offchain_primitives.go, and channel/manager.go, then search the documentation for other project-specific terms. Create a glossary that explains the referenced IDs and roles, along with other recurring terms, and ensure the meanings match their usage in the code and documentation.

Written by the indexing model from the issue text.