Update the deployments tab title to show the count

What does this MR do and why?

This MR adds the deployment count to the deployments history tab. It uses the newly added deployments_display_count field. The field returns an actual count up to 999 deployments and then returns 999+.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

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Before	After

In case of more than 1000 deployments, it will look like this:

In case there's no deployment, it will look like this:

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Visit Operate -> Environments and create an environment.
2. Create a deployment for the environment. To simplify that you could clone this project: https://gitlab.com/andrei.zubov/pipelinestest and run a few deployment pipelines.
3. Click on the newly created environment title to navigate to the environment detail page.
4. Verify the deployments list.

Related to #442820 (closed)