Add silence ping logging flag

Add ability to silence logging of requests to /ping endpoint, reducing
log clutter

Pros:
- Don't have to change all handlers to set/not set silent ping logging
- Don't have to duplicate `loggingHandler` (this could be preferable yet)

Cons:
- Leaking oauth2proxy logic into `package logger`
- Defining default pingPath in two locations

Alternative:
- Add generic exclude path to `logger.go` and pass in `/ping`.

options.go

@@ -103,6 +103,8 @@ type Options struct {
 	StandardLoggingFormat string `flag:"standard-logging-format" cfg:"standard_logging_format" env:"OAUTH2_PROXY_STANDARD_LOGGING_FORMAT"`
 	RequestLogging        bool   `flag:"request-logging" cfg:"request_logging" env:"OAUTH2_PROXY_REQUEST_LOGGING"`
 	RequestLoggingFormat  string `flag:"request-logging-format" cfg:"request_logging_format" env:"OAUTH2_PROXY_REQUEST_LOGGING_FORMAT"`
+	PingPath              string `flag:"ping-path" cfg:"ping_path" env:"OAUTH2_PROXY_PING_PATH"`
+	SilencePingLogging    bool   `flag:"silence-ping-logging" cfg:"silence_ping_logging" env:"OAUTH2_PROXY_SILENCE_PING_LOGGING"`
 	AuthLogging           bool   `flag:"auth-logging" cfg:"auth_logging" env:"OAUTH2_PROXY_LOGGING_AUTH_LOGGING"`
 	AuthLoggingFormat     string `flag:"auth-logging-format" cfg:"auth_logging_format" env:"OAUTH2_PROXY_AUTH_LOGGING_FORMAT"`
 
@@ -165,6 +167,8 @@ func NewOptions() *Options {
 		LoggingMaxBackups:                0,
 		LoggingLocalTime:                 true,
 		LoggingCompress:                  false,
+		PingPath:                         "/ping",
+		SilencePingLogging:               false,
 		StandardLogging:                  true,
 		StandardLoggingFormat:            logger.DefaultStandardLoggingFormat,
 		RequestLogging:                   true,
@@ -567,6 +571,8 @@ func setupLogger(o *Options, msgs []string) []string {
 	logger.SetStandardEnabled(o.StandardLogging)
 	logger.SetAuthEnabled(o.AuthLogging)
 	logger.SetReqEnabled(o.RequestLogging)
+	logger.SetSilentPing(o.SilencePingLogging)
+	logger.SetPingPath(o.PingPath)
 	logger.SetStandardTemplate(o.StandardLoggingFormat)
 	logger.SetAuthTemplate(o.AuthLoggingFormat)
 	logger.SetReqTemplate(o.RequestLoggingFormat)