Update OpenAPI Spec & Merge Files API (#139)

## Changes
This PR adds recent changes from OpenAPI to the Java SDK. Notably, it
adds support for the Files API. The integration test for this API can
only be run in UC workspaces, so this PR also adds support for UC-only
integration tests at the workspace- and account-level.

## Tests
- [x] New integration test for Files API to verify that it works as
expected.

Author: mgyucht

.codegen/_openapi_sha

@@ -1 +1 @@
-beff621d7b3e1d59244e2e34fc53a496f310e130
+be3d4a799362f0d5ddbfeb0a0acdfb91f8736a3b

.gitattributes

@@ -84,8 +84,9 @@ private Response computeResponse(Request in, CloseableHttpResponse response) thr
     boolean streamResponse =
         in.getHeaders().containsKey("Accept")
             && !APPLICATION_JSON.getMimeType().equals(in.getHeaders().get("Accept"))
-            && hs.containsKey("Content-Type")
-            && !APPLICATION_JSON.getMimeType().equals(hs.get("Content-Type").get(0));
+            && !APPLICATION_JSON
+                .getMimeType()
+                .equals(response.getFirstHeader("Content-Type").getValue());
     if (streamResponse) {
       CustomCloseInputStream inputStream =
           new CustomCloseInputStream(