feat: Conversation update API for sla_policy_id (#8973)

- Add an endpoint for updating conversation attributes (priority / sla_policy_id )
- Swagger spec
- minor chores around the conversation API/spec

Fixes: https://linear.app/chatwoot/issue/CW-2100/feat-backend-api-to-update-the-sla-of-a-conversation

swagger/paths/application/conversation/update.yml

@@ -0,0 +1,29 @@
+tags:
+  - Conversations
+operationId: update-conversation
+summary: Update Conversation
+description: Update Conversation Attributes
+security:
+  - userApiKey: []
+  - agentBotApiKey: []
+parameters:
+  - name: data
+    in: body
+    required: true
+    schema:
+      type: object
+      properties:
+        priority:
+          type: string
+          enum:  ["urgent", "high", "medium", "low", "none"]
+          description: "The priority of the conversation"
+        sla_policy_id:
+          type: number
+          description: "The ID of the SLA policy (Available only in Enterprise edition)"
+responses:
+  200:
+    description: Success
+  404:
+    description: Conversation not found
+  401:
+    description: Unauthorized