Add a OTEL_DEBUG env variable for enabling debug mode

[KyleAMathews]

Right now we use an OTEL_EXPORT variable for switching between debug mode & exporting to an opentelemetry service —

electric/packages/sync-service/config/runtime.exs

Lines 35 to 70 in 5cd4a95

	case otel_export do
	"otlp" ->
	if endpoint = env!("OTLP_ENDPOINT", :string, nil) do
	# Shortcut config for Honeycomb.io:
	# users may set the optional HNY_API_KEY and HNY_DATASET environment variables
	# and specify the Honeycomb URL in OTLP_ENDPOINT to export traces directly to
	# Honeycomb, without the need to run an OpenTelemetry Collector.
	honeycomb_api_key = env!("HNY_API_KEY", :string, nil)
	honeycomb_dataset = env!("HNY_DATASET", :string, nil)
	headers =
	Enum.reject(
	[
	{"x-honeycomb-team", honeycomb_api_key},
	{"x-honeycomb-dataset", honeycomb_dataset}
	],
	fn {_, val} -> is_nil(val) end
	)
	config :opentelemetry_exporter,
	otlp_protocol: :http_protobuf,
	otlp_endpoint: endpoint,
	otlp_headers: headers,
	otlp_compression: :gzip
	end
	"debug" ->
	# In this mode, each span is printed to stdout as soon as it ends, without batching.
	config :opentelemetry, :processors,
	otel_simple_processor: %{exporter: {:otel_exporter_stdout, []}}
	_ ->
	config :opentelemetry,
	processors: [],
	traces_exporter: :none
	end

Instead we should add an OTEL_DEBUG which enable debug mode and otherwise export if the other otel configuration is correct.