feat: add popover to users in flags list (#7344)

This PR adds a popover to the user avatars in the flag list.

The popover is similar to the one used for projects and groups, but it
differs in a few ways:
- There's less padding. There's quite a lot of padding in the other
popovers, and it felt like too much for this table.
- It only shows one bit of text (the user's name/username/email). The
other popovers show email and name/username, but we don't have all that
information, so this is a stripped down version.

Flag list popover:

![image](https://github.com/Unleash/unleash/assets/17786332/6a86f638-ba6d-48e0-87e2-078b582697cf)

Group popover:

![image](https://github.com/Unleash/unleash/assets/17786332/d5fc7172-8fcb-4fac-87c4-05f211c0938c)

or if no email

![image](https://github.com/Unleash/unleash/assets/17786332/51955ead-849f-4bfc-81aa-e1852677647c)

frontend/src/component/common/UserAvatar/UserAvatar.tsx

@@ -25,7 +25,7 @@ const StyledAvatar = styled(Avatar, {
     };
 });
 
-interface IUserAvatarProps extends AvatarProps {
+export interface IUserAvatarProps extends AvatarProps {
     user?: Partial<
         Pick<IUser, 'id' | 'name' | 'email' | 'username' | 'imageUrl'>
     >;
@@ -77,7 +77,7 @@ export const UserAvatar: FC<IUserAvatarProps> = ({
             sx={sx}
             {...props}
             data-loading
-            alt='Gravatar'
+            alt={user?.name || user?.email || user?.username || 'Gravatar'}
             src={src}
             title={title}
             onMouseEnter={onMouseEnter}

frontend/src/component/common/UserAvatar/UserAvatarWithPopover.tsx

@@ -0,0 +1,92 @@
+import { styled, Popover } from '@mui/material';
+import { useState, type FC } from 'react';
+import type React from 'react';
+import { type IUserAvatarProps, UserAvatar } from './UserAvatar';
+
+type PopoverProps = {
+    mainText: string;
+    open: boolean;
+    anchorEl: HTMLElement | null;
+    onPopoverClose(event: React.MouseEvent<HTMLElement>): void;
+};
+
+const StyledPopover = styled(Popover)(({ theme }) => ({
+    pointerEvents: 'none',
+    '.MuiPaper-root': {
+        padding: theme.spacing(1),
+    },
+}));
+
+const AvatarPopover = ({
+    mainText,
+    open,
+    anchorEl,
+    onPopoverClose,
+}: PopoverProps) => {
+    return (
+        <StyledPopover
+            open={open}
+            anchorEl={anchorEl}
+            onClose={onPopoverClose}
+            disableScrollLock={true}
+            disableRestoreFocus={true}
+            anchorOrigin={{
+                vertical: 'bottom',
+                horizontal: 'center',
+            }}
+            transformOrigin={{
+                vertical: 'top',
+                horizontal: 'center',
+            }}
+        >
+            <p>{mainText}</p>
+        </StyledPopover>
+    );
+};
+
+type UserAvatarWithPopoverProps = Omit<
+    IUserAvatarProps,
+    'user' | 'onMouseEnter' | 'onMouseLeave'
+> & {
+    user: {
+        name: string;
+        id?: number;
+        imageUrl?: string;
+    };
+};
+
+export const UserAvatarWithPopover: FC<UserAvatarWithPopoverProps> = ({
+    user,
+    ...userAvatarProps
+}) => {
+    const [anchorEl, setAnchorEl] = useState<HTMLElement | null>(null);
+    const onPopoverOpen = (event: React.MouseEvent<HTMLElement>) => {
+        setAnchorEl(event.currentTarget);
+    };
+
+    const onPopoverClose = () => {
+        setAnchorEl(null);
+    };
+
+    const avatarOpen = Boolean(anchorEl);
+
+    return (
+        <>
+            <UserAvatar
+                {...userAvatarProps}
+                user={user}
+                data-loading
+                onMouseEnter={(event) => {
+                    onPopoverOpen(event);
+                }}
+                onMouseLeave={onPopoverClose}
+            />
+            <AvatarPopover
+                mainText={user.name}
+                open={avatarOpen}
+                anchorEl={anchorEl}
+                onPopoverClose={onPopoverClose}
+            />
+        </>
+    );
+};

frontend/src/component/project/Project/PaginatedProjectFeatureToggles/ProjectFeatureToggles.tsx

@@ -39,7 +39,8 @@ import {
     useProjectFeatureSearch,
     useProjectFeatureSearchActions,
 } from './useProjectFeatureSearch';
-import { UserAvatar } from '../../../common/UserAvatar/UserAvatar';
+import { UserAvatarWithPopover } from '../../../common/UserAvatar/UserAvatarWithPopover';
+import type { Theme } from '@mui/material';
 
 interface IPaginatedProjectFeatureTogglesProps {
     environments: string[];
@@ -176,13 +177,15 @@ export const ProjectFeatureToggles = ({
                           header: 'By',
                           cell: ({ row: { original } }) => {
                               return (
-                                  <UserAvatar
+                                  <UserAvatarWithPopover
                                       user={{
                                           id: original.createdBy.id,
                                           name: original.createdBy.name,
                                           imageUrl: original.createdBy.imageUrl,
                                       }}
-                                      avatarWidth={(theme) => theme.spacing(3)}
+                                      avatarWidth={(theme: Theme) =>
+                                          theme.spacing(3)
+                                      }
                                   />
                               );
                           },