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/definitions/index.yml

@@ -223,6 +223,8 @@ account_summary:
   $ref: './resource/reports/summary.yml'
 agent_conversation_metrics:
   $ref: './resource/reports/conversation/agent.yml'
+channel_summary:
+  $ref: './resource/reports/channel_summary.yml'
 
 contact_detail:
   $ref: ./resource/contact_detail.yml

swagger/definitions/resource/reports/channel_summary.yml

@@ -0,0 +1,34 @@
+type: object
+description: Channel summary report containing conversation counts grouped by channel type and status. Available in version 4.10.0+.
+additionalProperties:
+  type: object
+  description: Conversation statistics for a specific channel type (e.g., Channel::WebWidget, Channel::Api)
+  properties:
+    open:
+      type: number
+      description: Number of open conversations
+    resolved:
+      type: number
+      description: Number of resolved conversations
+    pending:
+      type: number
+      description: Number of pending conversations
+    snoozed:
+      type: number
+      description: Number of snoozed conversations
+    total:
+      type: number
+      description: Total number of conversations
+example:
+  Channel::WebWidget:
+    open: 10
+    resolved: 20
+    pending: 5
+    snoozed: 2
+    total: 37
+  Channel::Api:
+    open: 5
+    resolved: 15
+    pending: 3
+    snoozed: 1
+    total: 24