Disable primary stickiness for WebHookService

What does this MR do?

This change disables primary stickiness in load balanced environments for the WebHookService response handler.

We hope that this will make it more likely for this worker to go to replicas for reads. Full context in this issue: #324376 (closed)

In short, we think that because these writes are merely logging and updating hook statistics, we won't be reading stale data even when going to replicas.

Note that I decided to put this behind the same FF as the load-balancing feature for the worker calling into this service (#331365 (closed)) since this is logically part of the same rollout. We disabled the feature for now because the results were not adequate, and are hoping that this additional change might make it more impactful. I will either roll back all changes or none.

Does this MR meet the acceptance criteria?

Conformity

• I have included a changelog entry, or it's not needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Related to #324376 (closed)