Fix process load test results workflow

[TharmiganK]

Purpose

The load-tests has been failing for some time due to the following issue:

• The merge PR step hangs intermittently and get timed-out, which makes the PR not merged until the next load test results PR
• Due to the above reason, there is already a load-test-results branch which is not sync with the master, which makes the push branch step fail

In this PR, the above issues has been addressed with the following changes:

• Use a github CLI command to wait until all the required checks pass
• Check for already existing branch and remove it before pushing the new changes - Ideally this check is not required when the PR is merged automatically

[ThisaruGuruge]

Check for already existing branch and remove it before pushing the new changes - Ideally this check is not required when the PR is merged automatically

I am -1 for this. We have discussed this previously as well. If a load test PR was failed due to a GitHub issue, we will lose that load test result because of this. The recommended way is to module owners to manually handle this (or maybe we can come up with a way to automate this, but I'm not sure).

Manually handling:

1. Close the failed PR
2. Delete the branch
3. Re-run the failed load test processing workflows

[TharmiganK]

I am -1 for this. We have discussed this previously as well. If a load test PR was failed due to a GitHub issue, we will lose that load test result because of this. The recommended way is to module owners to manually handle this (or maybe we can come up with a way to automate this, but I'm not sure).

Ack, will remove the deleting part.

May be we can send a notification to a notification chat group with the library team members, so that they can address it asap

[TharmiganK]

Since the workflows are failing currently in the merge PR step, I will merge this change and test. Sending notification on failure will be addressed separately