CLOUD-4725: document latency p50 fields, mark mean fields as aliases

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Px119CDnFd65gb49cZHzeH

Author: burak-upstash

devops/developer-api/openapi.yaml

@@ -2138,35 +2138,53 @@ components:
             $ref: "#/components/schemas/TimeSeriesData"
           description: Disk usage over time
           example: [{ "x": "2025-08-31 15:12:52.799480932 +0000 UTC", "y": 0 }]
+        latency_p50:
+          type: array
+          items:
+            $ref: "#/components/schemas/TimeSeriesData"
+          description: Median (p50) latency over time
+          example: [{ "x": "2025-08-31 15:12:52.799480932 +0000 UTC", "y": 0 }]
         latencymean:
           type: array
           items:
             $ref: "#/components/schemas/TimeSeriesData"
-          description: Average latency over time
+          description: Deprecated alias of latency_p50, kept for older clients. Carries the median, not the mean.
           example: [{ "x": "2025-08-31 15:12:52.799480932 +0000 UTC", "y": 0 }]
         latency_99:
           type: array
           items:
             $ref: "#/components/schemas/TimeSeriesData"
           description: 99th percentile latency over time
           example: [{ "x": "2025-08-31 15:12:52.799480932 +0000 UTC", "y": 0 }]
+        read_latency_p50:
+          type: array
+          items:
+            $ref: "#/components/schemas/TimeSeriesData"
+          description: Median (p50) read latency over time
+          example: [{ "x": "2025-08-31 15:12:52.799480932 +0000 UTC", "y": 0 }]
         read_latency_mean:
           type: array
           items:
             $ref: "#/components/schemas/TimeSeriesData"
-          description: Average read latency over time
+          description: Deprecated alias of read_latency_p50, kept for older clients. Carries the median, not the mean.
           example: [{ "x": "2025-08-31 15:12:52.799480932 +0000 UTC", "y": 0 }]
         read_latency_99:
           type: array
           items:
             $ref: "#/components/schemas/TimeSeriesData"
           description: 99th percentile read latency over time
           example: [{ "x": "2025-08-31 15:12:52.799480932 +0000 UTC", "y": 0 }]
+        write_latency_p50:
+          type: array
+          items:
+            $ref: "#/components/schemas/TimeSeriesData"
+          description: Median (p50) write latency over time
+          example: [{ "x": "2025-08-31 15:12:52.799480932 +0000 UTC", "y": 0 }]
         write_latency_mean:
           type: array
           items:
             $ref: "#/components/schemas/TimeSeriesData"
-          description: Average write latency over time
+          description: Deprecated alias of write_latency_p50, kept for older clients. Carries the median, not the mean.
           example: [{ "x": "2025-08-31 15:12:52.799480932 +0000 UTC", "y": 0 }]
         write_latency_99:
           type: array