Dry-run policies

### Is your feature request related to a problem?

Ability to dry-run policies to try out changes/new policies

### Describe the solution you'd like

Store the policy result data into the flow context (even if the policy is not in dry-run)

Allows inspection of the data from the inspector _after_ the policy ran, and not only of the policy result.
Allows custom expression policies from that data.

### Describe alternatives that you've considered

`ak_call_policy` from an expression policy. Does not give access to the policy data.

### Additional context

ref https://github.com/goauthentik/internal-customer-ref/issues/2

Start by tracing how policies run, how expression policies call ak_call_policy, and how the inspector reads flow context. Determine where policy result data can be retained for both dry-run and normal execution; done means the data is inspectable after execution and available to custom expression policies.

Written by the indexing model from the issue text.