feat: Add an API to support querying metrics by ChannelType (#13255)

This API gives you how many conversations exist per channel, broken down
by status in a given time period. The max time period is capped to 6
months for now.

**Input Params:**
- **since:** Unix timestamp (seconds) - start of date range
- **until:** Unix timestamp (seconds) - end of date range


**Response Payload:**

```json
{
  "Channel::Sms": {
    "resolved": 85,
    "snoozed": 10,
    "open": 5,
    "pending": 5,
    "total": 100
  },
  "Channel::Email": {
    "resolved": 72,
    "snoozed": 15,
    "open": 13,
    "pending": 13,
    "total": 100
  },
  "Channel::WebWidget": {
    "resolved": 90,
    "snoozed": 7,
    "open": 3,
    "pending": 3,
    "total": 100
  }
}
```

**Definitons:**
resolved = Number of conversations created within the selected time
period that are currently marked as resolved.
snoozed = Number of conversations created within the selected time
period that are currently marked as snoozed.
pending = Number of conversations created within the selected time
period that are currently marked as pending.
open = Number of conversations created within the selected time period
that are currently open.
total = Total number of conversations created within the selected time
period, across all statuses.

swagger/paths/index.yml

@@ -639,6 +639,28 @@
   get:
     $ref: './application/reports/conversation/agent.yml'
 
+# Channel summary report (Available in 4.10.0+)
+/api/v2/accounts/{account_id}/summary_reports/channel:
+  parameters:
+    - $ref: '#/components/parameters/account_id'
+    - in: query
+      name: since
+      schema:
+        type: string
+      description: The timestamp from where report should start (Unix timestamp).
+    - in: query
+      name: until
+      schema:
+        type: string
+      description: The timestamp from where report should stop (Unix timestamp).
+    - in: query
+      name: business_hours
+      schema:
+        type: boolean
+      description: Whether to filter by business hours.
+  get:
+    $ref: './application/reports/channel_summary.yml'
+
 # Conversations Messages
 /accounts/{account_id}/conversations/{conversation_id}/messages:
   parameters: