Add optional keyword to onboarding test job

[xwjiang-ms]

Description of PR

Summary:
Fixes # (issue)

Type of change

• Bug fix
• Testbed and Framework(new/improvement)
• Test case(new/improvement)

Back port request

• 202012
• 202205
• 202305
• 202311
• 202405

Approach

What is the motivation for this PR?

Onboarding test jobs are optional test jobs, we are using it in piloting, but some contributors were confused with failed onboarding jobs

How did you do it?

Add an optional keyword to reduce confusion

How did you verify/test it?

Any platform specific information?

Supported testbed topology if it's a new test case?

Documentation

[yutongzhang-microsoft]

Parameter STOP_ON_FAILURE: "False" and STOP_ON_FAILURE: "False" will promise this checker will always return success, unless the elastic test failed due to some transient issues. So, I think there is no confusion now.

[xwjiang-ms]

Parameter STOP_ON_FAILURE: "False" and STOP_ON_FAILURE: "False" will promise this checker will always return success, unless the elastic test failed due to some transient issues. So, I think there is no confusion now.

Parameter would not stop testplan, but testplan failure would still cause failure for onboarding jobs, like lock testbed failure, sanity check/testbed issue, so it's needed to add an optional keyword to reduce confusion