[ipcamera] Make sure created Servlet supports async (#14552)

[ipcamera] Make sure created Servlet supports async (#14552)

Fixes the folowing errors:

```
HTTP ERROR 500 java.lang.IllegalStateException: !asyncSupported: NotAsync:org.ops4j.pax.web.service.spi.servlet.OsgiInitializedServlet@536b0858
URI:	/ipcamera/192168493/ipcamera.jpg
STATUS:	500
MESSAGE:	java.lang.IllegalStateException: !asyncSupported: NotAsync:org.ops4j.pax.web.service.spi.servlet.OsgiInitializedServlet@536b0858
SERVLET:	org.openhab.binding.ipcamera.internal.servlet.CameraServlet
CAUSED BY:	java.lang.IllegalStateException: !asyncSupported: NotAsync:org.ops4j.pax.web.service.spi.servlet.OsgiInitializedServlet@536b0858
Powered by Jetty:// 9.4.50.v20221201
```

See:

* https://community.openhab.org/t/openhab-4-0-snapshot-discussion/142322/226
* https://groups.google.com/g/ops4j/c/E9p7tPydPmo
* https://github.com/ops4j/org.ops4j.pax.web/issues/1767

Signed-off-by: Wouter Born <github@maindrain.net>