inconsistency in resource vs. macro based route definition behaviour

Dieses Issue hat noch niemand übernommen.

When making:

```
curl -X POST \
'http://localhost:7777/foo?rule_name=foo.logic&force_overwrite=true&version=1.1' \
-H 'accept: application/json' \
-H 'cache-control: no-cache' \
-H 'content-type: text/plain' \
-d 'bla'
```

the following definition behaves correctly:

```
(POST "/foo" []
:middleware [[muuntaja.middleware/wrap-format
(muuntaja/create
(assoc-in muuntaja/default-options
[:formats "text/plain"] text-plain-format))]]
:query-params [version :- String, rule_name :- String, force_overwrite :- String]
:body [b s/Str]
:return s/Any
(ok
{:ok b})
```

on other hand this one is failing

```
(context "/foo" []
(resource {
:post {
:middleware [[muuntaja.middleware/wrap-format
(muuntaja/create
(assoc-in muuntaja/default-options
[:formats "text/plain"] text-plain-format))]]

:parameters {:body-params String
:query-params {:version s/Str
:rule_name s/Str
:force_overwrite s/Str}}
:consumes ["text/plain"]
:responses {http-status/ok {:schema s/Any}}
:handler (fn [{body :body-params {:keys [version rule_name]} :path-params}]
(ok
{:foo body}
))}}))

```

the error is:

```
{
"schema": "java.lang.String",
"errors": "(not (instance? java.lang.String nil))",
"type": "compojure.api.exception/request-validation",
"coercion": "schema",
"value": null,
"in": [
"request",
"body-params"
]
}
```

I use this auxiliary fun:
```

(def text-plain-format
{:decoder [(fn make-json-decoder [options]
(fn [x ^String charset]
(if (string? x)
x
(slurp (InputStreamReader. ^InputStream x charset)))))]

:encoder [(fn make-json-encoder [options]
(fn [data ^String charset]
(ByteArrayInputStream. (.getBytes data charset))))]})
```

Reproduziere die POST /foo curl-Anfrage und vergleiche dann die makrobasierte Route mit der Context-/Resource-Definition. Beginne bei der Validierung des Body-Parameters der Resource-Route und der benutzerdefinierten text/plain-Middleware; fertig ist es, wenn beide Routenformen dieselbe Anfrage konsistent verarbeiten, ohne den nil-String-Validierungsfehler.

Vom Indexierungsmodell aus dem Issue-Text verfasst.