fix(telemetry): remove Apdex middleware to align with go-monorepo

Remove the OpenTelemetryApdex middleware that creates redundant HTTP
server metrics. This aligns with go-monorepo PR #304 which removes the
same functionality.

Changes:
- Delete otel_apdex.go and otel_apdex_test.go
- Remove OpenTelemetryApdex middleware registration from httpserver.go
- Update otel_test.go to remove Apdex-related test cases
- Update telemetry.md to remove Apdex documentation

Eliminated metrics:
- keboola_go_http_server_apdex_count
- keboola_go_http_server_apdex_500_sum
- keboola_go_http_server_apdex_1000_sum
- keboola_go_http_server_apdex_2000_sum

Fixes PSGO-57

Co-Authored-By: Martin Vasko <Matovidlo2@gmail.com>

Author: devin-ai-integration[bot]

docs/telemetry.md

@@ -43,30 +43,6 @@ the [prometheus.ServeMetrics](../internal/pkg/telemetry/metric/prometheus/promet
 |-----------------------|--------------------------------------------------------------------------------------------------|
 | `http.server.request` | HTTP request. Attributes `keboola.*` contain info about stack, project and token, if applicable. |
 
-#### Apdex
-
-[Apdex](https://en.wikipedia.org/wiki/Apdex) metric measure user satisfaction as a value `0.0-1.0`:
-
-- Parameter `T` defines threshold for `satisfied` request duration in `ms`.
-- `4T` is threshold for `tolerating` request duration.
-- Longer durations are considered as `frustrated`, as well as requests with a status code `>= 500` (server errors).
-
-Apdex is reported cumulatively from [Go code](../internal/pkg/service/common/httpserver/middleware/otel_apdex.go).
-The following metrics are generated:
-
-| Span                                          | Description                           |
-|-----------------------------------------------|---------------------------------------|
-| `keboola_go_http_server_apdex_count.count`    | Apdex - total count of requests.      |
-| `keboola_go_http_server_apdex_500_sum.count`  | Apdex sum for: T=`500ms` 4T=`2000ms`  |
-| `keboola_go_http_server_apdex_1000_sum.count` | Apdex sum for: T=`1000ms` 4T=`4000ms` |
-| `keboola_go_http_server_apdex_2000_sum.count` | Apdex sum for: T=`2000ms` 4T=`8000ms` |
-
-Final Apdex value is calculated as follows:
-
-```
-keboola_go_http_server_apdex_<T>_sum.count / keboola_go_http_server_apdex_count.count
-```
-
 ## HTTP Client
 
 Client telemetry is implemented in the [keboola-sdk-go](https://github.com/keboola/keboola-sdk-go) repository, in

internal/pkg/service/common/httpserver/httpserver.go

@@ -59,7 +59,6 @@ func New(ctx context.Context, d dependencies, cfg Config) *HTTPServer {
 	middlewares = append(middlewares,
 		middleware.Logger(server.logger),
 		middleware.OpenTelemetry(tel.TracerProvider(), tel.MeterProvider(), middlewareCfg),
-		middleware.OpenTelemetryApdex(tel.MeterProvider()),
 	)
 
 	// Add gzip compression if enabled