Allow pattern matching on task signatures

Instead of doing a chain of if else if statements I think the justfile syntax would be cleaner if it supported pattern matching

```just
kubectl "staging" "app" *args:
Kubectl --context=dhdhdjd -n djdjsjdj-app {{ args }}

kubectl "prod" "app" *args:
# etcetc
```

Vs

```just
kubectl env service *args:
context = if env == "staging" { "djfjfnfn} # else if for every env
deployment = if app == # etc etc
```

Start by comparing the two task-signature examples and clarify the intended pattern-matching semantics, including how arguments and overlapping patterns should behave. Identify the relevant parser and task-signature tests in the repository; done means the proposed syntax is implemented with coverage for the examples and its edge cases.

Written by the indexing model from the issue text.