Issue with Jetty on POST/PUT/PATCH with empty content (consider disabling gzip all the time)

When a HTTP request has an empty content (no payload) for a POST/PUT/PATCH, a Jetty server fails with the following stack for a client request created by this API with the default parameters:
```
org.eclipse.jetty.http.BadMessageException: 501: Unsupported Content-Encoding
at org.eclipse.jetty.server.Request.extractContentParameters(Request.java:517)
at org.eclipse.jetty.server.Request.getParameters(Request.java:430)
at org.eclipse.jetty.server.Request.getParameter(Request.java:1059)
```
It fails to analyse parameters because the content-size is not set and the headers are not consistent. Here are the default headers:
```
Accept-Encoding: gzip
Authorization: Bearer ya29.a0AfH6SMDK...
User-Agent: Integration Tests Google-API-Java-Client/1.30.9 Google-HTTP-Java-Client/1.35.0 (gzip)
x-goog-api-client: gl-java/11.0.7 gdcl/1.30.9 linux/5.3.0
Content-Encoding: gzip
```
On a previous version of this lib, the Content-Size was set to 27, which is the compression of the empty content.

When the compression is disabled (`.setDisableGZipContent(true)`), the headers are ok and it works well with Jetty:
```
Accept-Encoding: gzip
Authorization: Bearer ya29.a0AfH6SMDK...
User-Agent: Integration Tests Google-API-Java-Client/1.30.9 Google-HTTP-Java-Client/1.35.0 (gzip)
x-goog-api-client: gl-java/11.0.7 gdcl/1.30.9 linux/5.3.0
Content-Length: 0
```

For this kind of request in particular, with empty content in general (when the content size can be determined), the field `disableGZipContent` in the class `AbstractGoogleClientRequest` should be ignored and the compression always disabled. This will avoid some tricky errors with the default parameters of an `AbstractGoogleClientRequest` and avoid unnecessary compression.

In `com.google.api.client.googleapis.services.AbstractGoogleClientRequest`, around line 426, there is a few lines handling this kind of request
```
// custom methods may use POST with no content but require a Content-Length header
if (httpContent == null && (requestMethod.equals(HttpMethods.POST)
|| requestMethod.equals(HttpMethods.PUT) || requestMethod.equals(HttpMethods.PATCH))) {
httpRequest.setContent(new EmptyContent());
}
```
You may force the disabling of the compression just after to really have the `Content-Length header`.