Avatar colored background code example

[szuperaz]

Add this to sample app, and create a code example guide:

Avatar: If possible, add a random color for the avatar’s bg. You can find 16 accessible colors here.

Implementation idea: create a custom avatar that users the default avatar component but sets background color dynamically

<ng-template
  #avatarTemplate
  let-name="name"
  let-imageUrl="imageUrl"
  let-size="size"
  let-user="user"
  let-channel="channel"
>
  <stream-avatar
    style="--str-chat__avatar-background-color: customColor"
    [name]="name"
    [imageUrl]="imageUrl"
    [size]="size"
    [user]="user"
    [channel]="channel"
  ></stream-avatar>
</ng-template>