🔥 limit::conditions and have Conditions be proper CEL Predicates

[alexsnaps]

So to leverage CEL consistently across all Kuadrant components

• Parse Limit's conditions as CEL expression (on creation)
• Parse Limit's variables as CEL expression (again, on creation)
• 🔥 feature lenient_conditions
• 🔥 module crate::limit::conditions
• Inject context about the Limit itself in the interpreter to enable e.g. Limit::id lookup (one context for the whole Limit, i.e. all conditions and all variables being resolved)
• Should the descriptor(s) and their entries be first class citizens and have their own root binding?