Updates admin credentials used in github workflow

[DarshitChanpura]

Description

This PR updates the occurrences of admin password in the github workflows. Coming from opensearch-project/security#3624, the security plugin recently introduced a change to require a custom strong password to be supplied when setting up the admin user via demo configuration.

Issues Resolved

• Resolves [v2.12.0] Ensure CI/documentation reflect changes to default admin credentials #515

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[RS146BIJAY]

I think there is one change in even README.md and build.gradle as well.

[DarshitChanpura]

updated all instances of admin credentials. This change should not be backported to <2.12 since the admin password changes are not required in those versions.

[DarshitChanpura]

Build failure seems to be unrelated:

* What went wrong:
A problem occurred configuring root project 'asynchronous-search'.
> java.util.concurrent.ExecutionException: org.gradle.api.GradleException: Failed to create Jar file /home/ci-runner/.gradle/caches/jars-9/6abf203a3d0[29](https://github.com/opensearch-project/asynchronous-search/actions/runs/7645086127/job/20830851711?pr=518#step:5:30)0f2fc6dc41dd82cb00d/jackson-core-2.16.1.jar.

[bharath-techie]

Hi @DarshitChanpura ,
Thanks for the changes.

We needed another change which include 2.12 BWC jar to make the build pass, so we had to raise a new PR and merge the changes.

Closing this PR for now.

[DarshitChanpura]

Sounds good @bharath-techie . The PR: #521
added a duplicate line in README that could be fixed.