Add reaction state to posts

[xla]

For client to reason if the user has reacted to a post with one of the available reactions we extend the Post representation with the has_reacted field which has a boolean for every of the possible reactions.

{
  ...
  "has_reacted": {
    "live": false,
    "love": false,
    "haha": true,
    ...
  },
  ...
}