Add grouping option to the key of the filtered-search

What does this MR do?

In this MR:

• Add to filtered-search component the ability to define grouping by keys titles), not just in the value as today.
• Update the Storybook accordingly.

As you can see here, we need to support grouping in the left side (keys) of the filtered-search .

References:

Issue link: gitlab-org/gitlab#537455 (closed)

Epic link: gitlab-org&16484

Design link: gitlab-org/gitlab#515955 (closed)

Screenshots or screen recordings

	Gitlab
Gitlab	Screen Recording 2025-06-26 at 13.16.01.mov
Gitlab
Storybook	Screen Recording 2025-06-27 at 8.38.45.mov
Storybook

Integrations

• GitLab: mr_url
• CustomersDot: mr_url
• Duo UI: mr_url
• Status Page: mr_url
• Docs: mr_url
• Switchboard: mr_url

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