fix(telemetry): fix grammer in time to first usable chunk metric (#5855)

## Problem
The grammar is bad in the unreleased first usable chunk metric

## Solution
Improve the grammar before we make the release

Author: jpinkney-aws

packages/core/src/codewhispererChat/controllers/chat/telemetryHelper.ts

@@ -450,7 +450,7 @@ export class CWCTelemetryHelper {
             ),
             cwsprChatFullResponseLatency: this.responseStreamTotalTime.get(message.tabID) ?? 0,
             cwsprChatTimeToFirstDisplay: this.getFirstDisplayTime(tabID, startTime),
-            cwsprChatTimeFirstUsableChunk: this.getFirstUsableChunkTime(message.tabID) ?? 0,
+            cwsprChatTimeToFirstUsableChunk: this.getFirstUsableChunkTime(message.tabID) ?? 0,
             cwsprChatFullServerResponseLatency: this.conversationStreamTotalTime.get(message.tabID) ?? 0,
             cwsprChatTimeBetweenDisplays: JSON.stringify(this.getTimeBetweenChunks(tabID, this.displayTimeForChunks)),
             cwsprChatFullDisplayLatency: fullDisplayLatency,

packages/core/src/shared/telemetry/vscodeTelemetry.json

@@ -170,7 +170,7 @@
             "description": "The time between when the conversation id was created and the final response from the server was received"
         },
         {
-            "name": "cwsprChatTimeFirstUsableChunk",
+            "name": "cwsprChatTimeToFirstUsableChunk",
             "type": "int",
             "description": "The time between the initial server request, including creating the conversation id, and the first usable result"
         },
@@ -763,7 +763,7 @@
                     "type": "cwsprChatFullResponseLatency"
                 },
                 {
-                    "type": "cwsprChatTimeFirstUsableChunk"
+                    "type": "cwsprChatTimeToFirstUsableChunk"
                 },
                 {
                     "type": "cwsprChatFullServerResponseLatency"