Use GlAvatar in approval rule selector

What does this MR do and why?

In the approvers list when adding an approval rule, we replace the deprecated project avatar with GlAvatarLabeled.

Related to #335524 (closed), for epic: &6295 (closed)

Screenshots or screen recordings

Before	After

How to set up and validate locally

Follow steps here: https://docs.gitlab.com/ee/user/project/merge_requests/approvals/rules.html#add-an-approval-rule

MR acceptance checklist

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