[Dashboard] Add flush() after job_id is populated

[LeoLiao123]

Why are these changes needed?

See the issue description and debugging details in ray-project/kuberay#3508.

Manual Test

command :

kubectl ray job submit\         
  --working-dir . \
  --name my-rayjob \
  --runtime-env-json='{"excludes":[
      "ray-operator/bin",
      "ray-operator/bin/k8s",
      ".git",
      "apiserver/pkg/swagger/datafile.go"
    ]}' \
  -- python task.py | ts '[%Y-%m-%d %H:%M:%S]'

task.py :

import time
import ray

ray.init(address="auto")

@ray.remote
def f():
    for i in range(20):
        print(i)
        time.sleep(1)
    return 1

print(ray.get([f.remote()]))

Result before adding flush()
Log output is delayed until after task.py completes :

my-rayjob remains in the Waiting state until the script finishes :

Result after adding flush()
Log output appears immediately after submission :

my-rayjob transitions to Running state right after submission.

Related issue number

Closes ray-project/kuberay#3508

Checks

• I've signed off every commit(by using the -s flag, i.e., git commit -s) in this PR.
• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://docs.ray.io/en/master/.
  • I've added any new APIs to the API Reference. For example, if I added a
    method in Tune, I've added it in doc/source/tune/api/ under the
    corresponding .rst file.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
  • Unit tests
  • Release tests
  • This PR is not tested :(

[LeoLiao123]

@MortalHappiness PTAL