Allow primitive and complex types in paths

[dumbbell]

Trying to store RabbitMQ bindings in Khepri appears to be difficult. A binding key is made of the #binding{} record itself. It is uneasy to split into multiple path components in Khepri because it contains a variable number of arguments.

We could convert the record to a binary, but it's not the best user experience. Ideally, we should allow complex structured types in Khepri paths so that the binding record can be stored as a path component directly.

There are several questions to answer while designing that change:

• The path API: how to store primitive & complex structures in a path without conflicting with ?ROOT_NODE-like macros (characters) and conditions (tuples)?
• How to represent them in a path string for the simpler API and in preparation of the OpenData REST API?
• What conditions could/should we add to do pattern matching on complex path components or comparisons with e.g. integer path components?