feat: support request_header key source (#4903)

* feat: support request_header key source in backend and settings UI

* feat: support request_header channel affinity source

web/default/src/features/system-settings/general/channel-affinity/rule-editor-dialog.tsx

@@ -50,7 +50,12 @@ import { Textarea } from '@/components/ui/textarea'
 import { RULE_TEMPLATES } from './constants'
 import type { AffinityRule, KeySource } from './types'
 
-const KEY_SOURCE_TYPES = ['context_int', 'context_string', 'gjson'] as const
+const KEY_SOURCE_TYPES = [
+  'context_int',
+  'context_string',
+  'request_header',
+  'gjson',
+] as const
 
 const CONTEXT_KEY_PRESETS = [
   'id',

web/default/src/features/system-settings/general/channel-affinity/types.ts

@@ -17,7 +17,7 @@ along with this program. If not, see <https://www.gnu.org/licenses/>.
 For commercial licensing, please contact support@quantumnous.com
 */
 export interface KeySource {
-  type: 'context_int' | 'context_string' | 'gjson'
+  type: 'context_int' | 'context_string' | 'request_header' | 'gjson'
   key?: string
   path?: string
 }