fix(ray): Use default svc account if not set in task metadata

[pingsutw]

Tracking issue

NA

Why are the changes needed?

The default service account is not being used if autoscale is enabled in the ray task.

What changes were proposed in this pull request?

Use default service account in the config if it's not being set.

How was this patch tested?

sandbox

Setup process

config = RayJobConfig(
    worker_node_config=[WorkerNodeConfig(group_name="test_group", replicas=3, min_replicas=0, max_replicas=10)],
    runtime_env={"pip": ["numpy"]},
    enable_autoscaling=True,
    shutdown_after_job_finishes=True,
    ttl_seconds_after_finished=20,
)

Screenshots

Check all the applicable boxes

• I updated the documentation accordingly.
• All new and existing tests passed.
• All commits are signed-off.

Related PRs

NA

Docs link

NA

[pingsutw]

cc @EngHabu @hamersaw @fiedlerNr9

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 60.99%. Comparing base (c10346d) to head (417a3a3).
Report is 132 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5499      +/-   ##
==========================================
- Coverage   61.01%   60.99%   -0.03%     
==========================================
  Files         794      794              
  Lines       51441    51443       +2     
==========================================
- Hits        31388    31378      -10     
- Misses      17161    17172      +11     
- Partials     2892     2893       +1     

Flag	Coverage Δ
unittests-datacatalog	69.31% <ø> (ø)
unittests-flyteadmin	58.67% <ø> (-0.07%)	⬇️
unittests-flytecopilot	17.79% <ø> (ø)
unittests-flytectl	68.03% <ø> (-0.06%)	⬇️
unittests-flyteidl	79.04% <ø> (ø)
unittests-flyteplugins	61.85% <100.00%> (+<0.01%)	⬆️
unittests-flytepropeller	57.30% <ø> (ø)
unittests-flytestdlib	65.82% <ø> (ø)

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