Enable ARM64 build with use_connext_debs for rmw_connext

[lobolanja]

Description

rmw_connext task: ros2/rmw_connextdds#222

Motivation

Update the CI to enable building rmw_connextdds for ARM64 on Ubuntu. Since we previously provided ARM packages through rti-connext-dds-7.3.0-ros, enabling this build would allow users to install the Connext RMW implementation directly instead of building it from source when running on ARM machines.

Design / Implementation Considerations

• Remove platform from  Dockerfile in CI
• Remove  ingnore_rmw_default in arch64 in line 148 in create_jenkins_job.py
• Entry_point.sh remove  if [ "${ARCH}" = "x86_64" -a

Additional Information

No response