Tests that should be run as helper tests are being run as webhooks plugin tests.

[yk634]

What happened:
The issue is caused by the merging of #2622.

In this PR, much of the processing of the webhooks plugin has been consolidated into the helper, which is shared with the processHooks plugin.
With this change, we will have to migrate most of the cases that were tested as webhooks plugin to helper tests.

If the tests is not migrated:

• Tests running as webhooks plugins make it difficult to know what they are testing (webhooks plugin or helper).
• When the helper is modified, it will be difficult to find the test target to be modified.

In this PR, we have migrated only some cases that are easy to migrate, but many cases still need to be migrated.

What you expected to happen:
The tests of the webhooks plugin that should be migrated will be migrated to the tests of the helper.

How to reproduce it:
This is not a bug but an issue that need to be refactored.

[yk634]

Migration sample.
https://github.com/sonic-screwdriver-cd/screwdriver/compare/use-queueservice-for-webhook...sonic-screwdriver-cd:migration-webhooks-test?expand=1