Fix race condition in apex-editor model upload

Fix race condition in apex-editor model upload

Fixed a race condition in /Model/Upload endpoint caused by userId
 query param overwriting a global parameter. New behavior is for
 userId to override global param for that request only.
Updated JavaDocs to reflect behavior.
Added JUnit test to verify userId overriding.
Fixed issue where upload success message was not included in response.

Issue-ID: POLICY-3929
Signed-off-by: danielhanrahan <daniel.hanrahan@est.tech>
Change-Id: Ic1d78083778eef2df3675b3b4fbc1e41420da46f