nix(loadtest): merge jwt-rsa-* and jwt-hs-* tests

Instead of creating separate test suites for the key type, the PostgREST
instance now accepts both keys via a JWKSet and the targets are
generated 50/50 for both.

The results are still reported seperately by using a different URL,
which shows up as separate rows in the results.

.github/workflows/test.yaml

@@ -131,7 +131,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        kind: ['mixed', 'jwt-hs', 'jwt-hs-cache', 'jwt-hs-cache-worst', 'jwt-rsa', 'jwt-rsa-cache', 'jwt-rsa-cache-worst']
+        kind: ['mixed', 'jwt', 'jwt-cache', 'jwt-cache-worst']
     name: Loadtest
     runs-on: ubuntu-24.04
     steps: