[feature] Initial Prometheus metrics implementation (#2334)

* feat: Initial OTEL metrics

* docs: add metrics documentation

* fix: metrics endpoint conditional check

* feat: metrics endpoint basic auth

* fix: make metrics-auth-enabled default false

* fix: go fmt helpers.gen.go

* fix: add metric-related env vars to envparsing.sh

* fix: metrics docs

* fix: metrics related stuff in envparsing.sh

* fix: metrics docs

* chore: metrics docs wording

* fix: metrics stuff in envparsing?

* bump otel versions

---------

Co-authored-by: Tsuribori <user@acertaindebian>
Co-authored-by: Tsuribori <none@example.org>
Co-authored-by: tsmethurst <tobi.smethurst@protonmail.com>

internal/config/config.go

@@ -140,6 +140,11 @@ type Configuration struct {
 	TracingEndpoint          string `name:"tracing-endpoint" usage:"Endpoint of your trace collector. Eg., 'localhost:4317' for gRPC, 'localhost:4318' for http"`
 	TracingInsecureTransport bool   `name:"tracing-insecure-transport" usage:"Disable TLS for the gRPC or HTTP transport protocol"`
 
+	MetricsEnabled      bool   `name:"metrics-enabled" usage:"Enable OpenTelemetry based metrics support."`
+	MetricsAuthEnabled  bool   `name:"metrics-auth-enabled" usage:"Enable HTTP Basic Authentication for Prometheus metrics endpoint"`
+	MetricsAuthUsername string `name:"metrics-auth-username" usage:"Username for Prometheus metrics endpoint"`
+	MetricsAuthPassword string `name:"metrics-auth-password" usage:"Password for Prometheus metrics endpoint"`
+
 	SMTPHost               string `name:"smtp-host" usage:"Host of the smtp server. Eg., 'smtp.eu.mailgun.org'"`
 	SMTPPort               int    `name:"smtp-port" usage:"Port of the smtp server. Eg., 587"`
 	SMTPUsername           string `name:"smtp-username" usage:"Username to authenticate with the smtp server as. Eg., 'postmaster@mail.example.org'"`