[CI] Update elastictest template and test_plan.py not to use CLIENT secret

[lerry-lee]

Description of PR

Update elastictest template and test_plan.py not to use CLIENT secret

This is part of the security wave 1 effort for eliminating CLIENT secrets. The test_plan.py script has been improved to get ACCESS_TOKEN from environment variable.

Signed-off-by: Chun'ang Li chunangli@microsoft.com

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?

How did you do it?

How did you verify/test it?

Any platform specific information?

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

Documentation

[wangxin]

There is already a fix for the issue: https://github.com/sonic-net/sonic-mgmt/pull/13440