Add option to set image_url ("background image") for user

While this option is not used anywhere in microblog.pub itself, some
other servers do occasionally use it when showing remote profiles.

Also, this image _can_ be used in microblog.pub - just add this:

	<img src="{{ local_actor.image_url }}">

in the appropriate place of your template!

app/activitypub.py

@@ -154,6 +154,12 @@ if ALSO_KNOWN_AS:
 if MOVED_TO:
     ME["movedTo"] = MOVED_TO
 
+if config.CONFIG.image_url:
+    ME["image"] = {
+        "mediaType": mimetypes.guess_type(config.CONFIG.image_url)[0],
+        "type": "Image",
+        "url": config.CONFIG.image_url,
+    }
 
 class NotAnObjectError(Exception):
     def __init__(self, url: str, resp: httpx.Response | None = None) -> None:

app/actor.py

@@ -88,6 +88,10 @@ class Actor:
     def icon_media_type(self) -> str | None:
         return self.ap_actor.get("icon", {}).get("mediaType")
 
+    @property
+    def image_url(self) -> str | None:
+        return self.ap_actor.get("image", {}).get("url")
+
     @property
     def public_key_as_pem(self) -> str:
         return self.ap_actor["publicKey"]["publicKeyPem"]
@@ -381,6 +385,9 @@ def _actor_hash(actor: Actor) -> bytes:
     if actor.icon_url:
         h.update(actor.icon_url.encode())
 
+    if actor.image_url:
+        h.update(actor.image_url.encode())
+
     if actor.attachments:
         for a in actor.attachments:
             if a.get("type") != "PropertyValue":

app/config.py

@@ -92,6 +92,7 @@ class Config(pydantic.BaseModel):
     summary: str
     https: bool
     icon_url: str
+    image_url: str
     secret: str
     debug: bool = False
     trusted_hosts: list[str] = ["127.0.0.1"]