fix: handle unrecognized JumpStart container images in ModelBuilder (#5818)

Collapse endpoint mode routing into a single code path since all
JumpStart builders (DJL, TGI, MMS) perform identical operations
for endpoint deployment. Unknown container images (e.g. vLLM) now
pass through instead of raising ValueError.

For local container mode, unrecognized images raise ValueError with
a message directing users to use SAGEMAKER_ENDPOINT mode.

Co-authored-by: Liam Neal Reilly <lnealrei@amazon.com>

Author: lhnealreilly