fix: Change otel env var

[Eric-Warehime]

Description

Fixes otel env var initialization via otelconf.

In this patch they changed the production env var and deprecated the old one--it returns an error now.

Closes: #XXXX

[greptile-apps]

Greptile Summary

This PR updates the OpenTelemetry configuration environment variable name from OTEL_EXPERIMENTAL_CONFIG_FILE to OTEL_CONFIG_FILE in response to an upstream breaking change in the opentelemetry-go-contrib library, which deprecated the old variable and now returns an error for it.

• telemetry/config.go: Updates the otelConfigEnvVar constant and the GoDoc comment to use OTEL_CONFIG_FILE.
• telemetry/README.md: Updates two references in the documentation to use the new env var name.

Confidence Score: 5/5

Safe to merge — the change is a straightforward one-line constant rename that aligns the codebase with a breaking upstream change in the otelconf library.

Both code and documentation are updated consistently, no stale references to the old env var remain anywhere in the repo, and the fix directly unblocks users who would otherwise hit an error from the deprecated variable.

No files require special attention.

Important Files Changed

Filename	Overview
telemetry/config.go	Renames otelConfigEnvVar constant from OTEL_EXPERIMENTAL_CONFIG_FILE to OTEL_CONFIG_FILE and updates the inline comment; change is minimal and correct.
telemetry/README.md	Updates two documentation references to the env var name to match the new OTEL_CONFIG_FILE value; no issues found.

Sequence Diagram

sequenceDiagram
    participant User
    participant OS as OS Environment
    participant init as telemetry init()
    participant SDK as otelconf.SDK

    User->>OS: export OTEL_CONFIG_FILE=path/to/config.yaml
    Note over OS: (previously OTEL_EXPERIMENTAL_CONFIG_FILE)
    init->>OS: os.Getenv("OTEL_CONFIG_FILE")
    OS-->>init: filePath (non-empty)
    init->>init: InitializeOpenTelemetry(filePath)
    init->>SDK: otelconf.NewSDK(opts...)
    SDK-->>init: otelSDK
    init->>init: Set global TracerProvider / MeterProvider / LoggerProvider

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_{Reviews (1): Last reviewed commit: "Change otel env var" | Re-trigger Greptile}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 64.87%. Comparing base (e77c24c) to head (a111639).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #26390      +/-   ##
==========================================
- Coverage   64.88%   64.87%   -0.02%     
==========================================
  Files         890      874      -16     
  Lines       58583    57601     -982     
==========================================
- Hits        38011    37367     -644     
+ Misses      20572    20234     -338     

Files with missing lines	Coverage Δ
telemetry/config.go	2.38% <ø> (ø)

... and 23 files with indirect coverage changes

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