[MastoAPI] Add switching of frontend flavours

docs/Pleroma-API.md

@@ -94,3 +94,17 @@ Request parameters can be passed via [query strings](https://en.wikipedia.org/wi
 
 ## `/api/pleroma/admin/`…
 See [Admin-API](Admin-API.md)
+
+## `/api/v1/pleroma/flavour/:flavour`
+* Method `POST`
+* Authentication: required
+* Response: JSON string. Returns the user flavour or the default one on success, otherwise returns `{"error": "error_msg"}`
+* Example response: "glitch"
+* Note: This is intended to be used only by mastofe
+
+## `/api/v1/pleroma/flavour`
+* Method `GET`
+* Authentication: required
+* Response: JSON string. Returns the user flavour or the default one.
+* Example response: "glitch"
+* Note: This is intended to be used only by mastofe