add doc for the profile_chunk item type (#11264)

Author: viglia

develop-docs/sdk/envelopes.mdx

@@ -597,6 +597,23 @@ in JSON.
 
 *None*
 
+### Profile Chunk
+
+Item type `"profile_chunk"`. This Item contains a profile_chunk (profile sample format V2) payload encoded
+in JSON.
+
+**Constraints:**
+
+*None*
+
+**Envelope Headers:**
+
+*None*
+
+**Additional Item Headers:**
+
+*None*
+
 ### Check-Ins
 
 Item type `"check_in"` contains a check-in payload encoded as JSON.

develop-docs/sdk/telemetry/profiles/sample-format-v2.mdx

@@ -291,7 +291,7 @@ It's suggested to remove unnecessary data like thread data without samples from
 ## Ingestion
 
 After this payload is generated, serialize it as JSON, pack it into an
-[Envelope](/sdk/envelopes/) with the item type `profile_chunk` and send 
+[Envelope](/sdk/envelopes/) with the item type [`profile_chunk`](/sdk/envelopes/#profile-chunk) and send 
 it to Relay.
 
 This envelope should look like this: