Prepare for tombstone support

[melroy89]

• Do not fail on 410 status code (used for Tombstone)
• Read also 410 error status HTTP content (which contains the tombstone object), passing false to getContent()
• Do not throw error / 500 error message

[melroy89]

You wanna test? sure try this tombstone url: https://lemm.ee/post/2871450

{
  "@context": [
    "https://www.w3.org/ns/activitystreams",
    "https://w3id.org/security/v1",
    {
      "lemmy": "https://join-lemmy.org/ns#",
      "litepub": "http://litepub.social/ns#",
      "pt": "https://joinpeertube.org/ns#",
      "sc": "http://schema.org/",
      "ChatMessage": "litepub:ChatMessage",
      "commentsEnabled": "pt:commentsEnabled",
      "sensitive": "as:sensitive",
      "matrixUserId": "lemmy:matrixUserId",
      "postingRestrictedToMods": "lemmy:postingRestrictedToMods",
      "removeData": "lemmy:removeData",
      "stickied": "lemmy:stickied",
      "moderators": {
        "@type": "@id",
        "@id": "lemmy:moderators"
      },
      "expires": "as:endTime",
      "distinguished": "lemmy:distinguished",
      "language": "sc:inLanguage",
      "identifier": "sc:identifier"
    }
  ],
  "id": "https://lemm.ee/post/2871450",
  "type": "Tombstone"
}

[nobodyatroot]

Less 500s, more better.

[melroy89]

We still need to improve the fetching (making it blocking fetch) and after that, we can improve the frontend, informing the user that this post/thread/.. is no longer there in case of a tombstone.