chore(feat): Add Github Action bot for litmus e2e runs on PR comment basis

[uditgaurav]

Signed-off-by: Udit Gaurav udit.gaurav@mayadata.io

What this PR does / why we need it:

• This PR will add Github action bot for running BDDs per experiment or all the experiments depending upon the changes in the pull request. For running the e2e tests for the experiment we just need to add a comment in the format /run-e2e-<experiment-name> like for running pod-delete BDDs we just need to add /run-e2e-pod-delete. Similarly for running all the BDDs for all the experiments we have to use /run-e2e-all.
• This will help in gaining confidence before merging a Pull Request as the tests will be performed on the basis of the last commit in the pull request.

Which issue this PR fixes

• fixes Run e2e tests for a particular experiment or all experiments depending upon the nature of the change before merging PRs in litmus using bot #1531

Checklist

• Does this PR have a corresponding GitHub issue?
• Have you included relevant README for the chaoslib/experiment with details?
• Have you added debug messages where necessary?
• Have you added task comments where necessary?
• Have you tested the changes for possible failure conditions?
• Have you provided the positive & negative test logs for the litmusbook execution?
• Does the litmusbook ensure idempotency of cluster state?, i.e., is cluster restored to original state?
• Have you used non-shell/command modules for Kubernetes tasks?
• Have you (jinja) templatized custom scripts that is run by the litmusbook, if any?
• Have you (jinja) templatized Kubernetes deployment manifests used by the litmusbook, if any?
• Have you reused/created util functions instead of repeating tasks in the litmusbook?
• Do the artifacts follow the appropriate directory structure?
• Have you isolated storage (eg: OpenEBS) specific implementations, checks?
• Have you isolated platform (eg: baremetal kubeadm/openshift/aws/gcloud) specific implementations, checks?
• Are the ansible facts well defined? Is the scope explicitly set for playbook & included utils?
• Have you ensured minimum/careful usage of shell utilities (awk, grep, sed, cut, xargs etc.,)?
• Can the limtusbook be executed both from within & outside a container (configurable paths, no hardcode)?
• Can you suggest the minimal resource requirements for the litmusbook execution?
• Does the litmusbook job artifact carry comments/default options/range for the ENV tunables?
• Has the litmusbooks been linted?

Special notes for your reviewer:

• The sample application created is nginx application, after creation of the application we are waiting for 30sec to get it ready this value is hardcoded just to avoid any external script. Please let me know if it's fine.
• There should be DUSER and DPASS containing the username and password of litmuschaos docker hub in Github secret.