Fixes https://github.com/spring-projects/spring-integration/issues/3827
The `AbstractRemoteFileOutboundGateway.doGet()` for a `STREAM` option
does not close the `session` in case of error.
This may lead to some leaks or exhausted caches
* Close `session` in the `catch()` of the `AbstractRemoteFileOutboundGateway.doGet()`
* Adjust the `SftpServerOutboundTests` to configure a `CachingSessionFactory`
for the `testStream()` to verify there is no leaks attempting to
`GET STREAM` non-existing remote file twice
**Cherry-pick to `5.5.x`**
8f44870837