Google Chat integration manual threadLink parameter is no longer working

Hi team, due to the recent changes made in #27823 (closed) and gitlab-com/www-gitlab-com!110654 (merged) the threadKey provided by the user is completely ignored and replaced with the auto-generated thready key by GitLab Google chat integration.

How to reproduce

1. Go to any repository in a GitLab instance
2. Go to Google Chat integration settings
3. Set the following value as the Webhook value:

https://chat.googleapis.com/v1/spaces/AAAA_2JVWqs/messages?key=<key>&token=<token>&threadKey=gitlabBotThread

Expected Results

• All the GitLab Notification should appear on the same thread that is specified by the threadKey regardless of the event if the user had specified the threadKey parameter in the webhook url

Actual Result

• GitLab now ignores the threadKey parameter specified by the user in the webhook URL and creates its own threadKey based on the event type. This results in the creation of a new thread whenever a specific type of event happens

Use Case

We have a common Google Chat Space for Devs and QEs. We used a specific thread in that space to notify the group of devs about the MR statuses. Since QEs are also in the same space they can also keep track of the exact same notifications. This was working just fine until recently. Since the changes made on #27823 (closed) were released, this is broken.