Migrate OTEL config to use generic field framework

[JAORMX]

Summary

Refactors OpenTelemetry configuration commands to use the generic config field framework introduced in #2483, demonstrating the framework's value by eliminating ~450 lines of boilerplate code.

Note: This PR is based on #2483 and includes those commits. It should be reviewed after #2483 is merged. The actual changes in this PR are only in the most recent commit.

Changes

New OTEL Field Registrations (pkg/config/fields_otel.go)

Registers 7 OTEL fields with the generic framework:

• otel-endpoint: OTLP endpoint URL with protocol validation
• otel-sampling-rate: Sampling rate with 0.0-1.0 range validation
• otel-env-vars: Comma-separated environment variables
• otel-metrics-enabled: Boolean metrics export flag
• otel-tracing-enabled: Boolean tracing export flag
• otel-insecure: Boolean insecure connection flag
• otel-enable-prometheus-metrics-path: Boolean Prometheus metrics path flag

Refactored Commands (cmd/thv/app/otel.go)

• Before: 577 lines with 18 hand-written command functions (set/get/unset × 7 fields)
• After: 127 lines with 3 generic command generators
• Reduction: 450 lines removed (78% reduction)

Replaced boilerplate functions with three generic helpers:

• createOTELSetCommand() - Generic set command generator
• createOTELGetCommand() - Generic get command generator
• createOTELUnsetCommand() - Generic unset command generator

Benefits

✅ Dramatic Code Reduction: 78% less code (577 → 127 lines)
✅ Consistent Behavior: All commands use the same framework logic
✅ Easier Maintenance: Changes to validation/error handling apply to all fields
✅ Proven Pattern: Same approach used for ca-cert, registry-url, registry-file
✅ No Behavioral Changes: All OTEL commands work identically

Before & After

Before (per field):

func setOtelEndpointCmdFunc(_ *cobra.Command, args []string) error {
    endpoint := args[0]
    if endpoint != "" && (strings.HasPrefix(endpoint, "http://") || strings.HasPrefix(endpoint, "https://")) {
        return fmt.Errorf("endpoint URL should not start with http:// or https://")
    }
    err := config.UpdateConfig(func(c *config.Config) {
        c.OTEL.Endpoint = endpoint
    })
    if err != nil {
        return fmt.Errorf("failed to update configuration: %w", err)
    }
    fmt.Printf("Successfully set OpenTelemetry endpoint: %s\n", endpoint)
    return nil
}
// + getOtelEndpointCmdFunc + unsetOtelEndpointCmdFunc
// × 7 fields = 21 functions

After (all fields):

RegisterConfigField(ConfigFieldSpec{
    Name: "otel-endpoint",
    SetValidator: func(_ Provider, value string) error {
        if value != "" && (strings.HasPrefix(value, "http://") || strings.HasPrefix(value, "https://")) {
            return fmt.Errorf("endpoint URL should not start with http:// or https://")
        }
        return nil
    },
    Setter: func(cfg *Config, value string) { cfg.OTEL.Endpoint = value },
    Getter: func(cfg *Config) string { return cfg.OTEL.Endpoint },
    Unsetter: func(cfg *Config) { cfg.OTEL.Endpoint = "" },
    // ... metadata
})

// Commands generated automatically via framework
OtelCmd.AddCommand(createOTELSetCommand("otel-endpoint", "endpoint", "endpoint URL", "https://api.honeycomb.io"))

Test Plan

• All config tests pass
• Build successful
• OTEL commands generate correctly (verified via --help)
• No behavioral changes to existing commands

Dependencies

Depends on #2483 - This PR is stacked on top of the config field framework PR. Review #2483 first.

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 18.58974% with 127 lines in your changes missing coverage. Please review.
✅ Project coverage is 54.98%. Comparing base (1a45143) to head (e917164).

Files with missing lines	Patch %	Lines
pkg/config/fields_otel.go	18.58%	120 Missing and 7 partials ⚠️

Additional details and impacted files

@@                       Coverage Diff                       @@
##           feat/config-field-framework    #2486      +/-   ##
===============================================================
- Coverage                        55.19%   54.98%   -0.21%     
===============================================================
  Files                              294      295       +1     
  Lines                            28060    28209     +149     
===============================================================
+ Hits                             15487    15510      +23     
- Misses                           11163    11283     +120     
- Partials                          1410     1416       +6     

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