Confusing display of custom power level in room user list

### Steps to reproduce

1. Go to a room that was migrated from Gitter, e.g. https://app.gitter.im/#/room/#ADOdb_ADOdb:gitter.im
2. In the room's People list, notice that users who previously were admins before Gitter migrated to Matrix, are now listed as *Mods*. However, @MadLittleMods informed me that they effectively are Admins, but with a Custom power level of **90** (see [discussion thread](https://matrix.to/#/!IxQMqGgyzZgHKssexF:gitter.im/$5OBWedojqUtnt-S18OT-WAspbZlRbCfxuL6beXvEOuU?via=gitter.im&via=matrix.org&via=aria-net.org)).
4. Invite a new user, and make them *Moderator*
6. In the user list, they are shown as **Mod** just like the old admins, but in reality their Power level is **50**



`m.room.power_levels` in room for example (all actions can be accomplished by a user with a power level of `90`):

```json
{
"ban": 50,
"events": {
"m.room.avatar": 50,
"m.room.canonical_alias": 50,
"m.room.encryption": 90,
"m.room.history_visibility": 90,
"m.room.name": 50,
"m.room.power_levels": 90,
"m.room.server_acl": 90,
"m.room.tombstone": 90
},
"events_default": 0,
"invite": 0,
"kick": 50,
"redact": 50,
"state_default": 50,
"users": {
"@dregad-544c57d4db8155e6700ce750:gitter.im": 90,
"@dregad:matrix.org": 90,
"@gitter-badger:gitter.im": 100,
"@mnewnham-5593f15f15522ed4b3e32b93:gitter.im": 90,
"@moderation:gitter.im": 100
},
"users_default": 0
}
```

### Outcome

#### What did you expect?

The People list should display the user's actual power level, and definitely **not** regroup custom power levels with standard ones, which is confusing (and misleading).

#### What happened instead?

Custom power level 90 is displayed as `Mod`

### Operating system

Windows

### Browser information

Firefox 102.4.0esr

### URL for webapp

app.gitter.im and app.element.io

### Application version

Version de Gitter : 1.11.23-rc.1 Version de Olm : 3.2.12 / Version de Element : 1.11.23 Version de Olm : 3.2.12

### Homeserver

gitter.im and matrix.org

### Will you send logs?

No

Start with the People list and the m.room.power_levels data described in the issue, comparing users at power levels 50 and 90. The change is complete when custom levels are not grouped under the standard Mod label and the displayed role accurately reflects the user's actual power level.

Written by the indexing model from the issue text.