Migrate OTEL config to use generic field framework

Refactor OpenTelemetry configuration commands to use the generic config
field framework, eliminating ~450 lines of boilerplate code.

Changes:
- Add OTEL field registrations using helper constructors
- Replace 18 hand-written command functions with 3 generic helpers
- Reduce cmd/thv/app/otel.go from 577 lines to 127 lines (78% reduction)
- Reduce pkg/config/fields_otel.go to 92 lines using RegisterBoolField,
  RegisterStringField, RegisterFloatField, and RegisterStringSliceField helpers

All OTEL commands maintain identical behavior with consistent validation
and error messages through the framework.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: JAORMX