feat: add mock telemetry server for local development (#21932)

Adds a standalone command that acts as a mock telemetry server,
receiving snapshots and printing them as a JSON stream to stdout. Useful
for local development testing with scripts/develop.sh by setting
CODER_TELEMETRY_ENABLE and CODER_TELEMETRY_URL environment variabless.

codersdk/deployment.go

@@ -2380,6 +2380,8 @@ func (c *DeploymentValues) Options() serpent.OptionSet {
 			Group:      &deploymentGroupTelemetry,
 			UseInstead: []serpent.Option{telemetryEnable},
 		},
+		// For local development testing, see scripts/telemetry-server which
+		// provides a mock server that prints received telemetry as JSON.
 		{
 			Name:        "Telemetry URL",
 			Description: "URL to send telemetry.",