MM-25731 Advanced Logging (#14888)

Adds Advanced Logging to server. Advanced Logging is an optional logging capability that allows customers to send log records to any number of destinations.

Supported destinations:
- file
- syslog (with out without TLS)
- raw TCP socket (with out without TLS)

Allows developers to specify discrete log levels as well as the standard trace, debug, info, ... panic. Existing code and logging API usage is unchanged.

Log records are emitted asynchronously to reduce latency to the caller. Supports hot-reloading of logger config, including adding removing targets.

Advanced Logging is configured within config.json via "LogSettings.AdvancedLoggingConfig" which can contain a filespec to another config file, a database DSN, or JSON.

vendor/github.com/mattermost/logr/levelstd.go

@@ -0,0 +1,37 @@
+package logr
+
+// StdFilter allows targets to filter via classic log levels where any level
+// beyond a certain verbosity/severity is enabled.
+type StdFilter struct {
+	Lvl        Level
+	Stacktrace Level
+}
+
+// IsEnabled returns true if the specified Level is at or above this verbosity. Also
+// determines if a stack trace is required.
+func (lt StdFilter) IsEnabled(level Level) bool {
+	return level.ID <= lt.Lvl.ID
+}
+
+// IsStacktraceEnabled returns true if the specified Level requires a stack trace.
+func (lt StdFilter) IsStacktraceEnabled(level Level) bool {
+	return level.ID <= lt.Stacktrace.ID
+}
+
+var (
+	// Panic is the highest level of severity. Logs the message and then panics.
+	Panic = Level{ID: 0, Name: "panic"}
+	// Fatal designates a catastrophic error. Logs the message and then calls
+	// `logr.Exit(1)`.
+	Fatal = Level{ID: 1, Name: "fatal"}
+	// Error designates a serious but possibly recoverable error.
+	Error = Level{ID: 2, Name: "error"}
+	// Warn designates non-critical error.
+	Warn = Level{ID: 3, Name: "warn"}
+	// Info designates information regarding application events.
+	Info = Level{ID: 4, Name: "info"}
+	// Debug designates verbose information typically used for debugging.
+	Debug = Level{ID: 5, Name: "debug"}
+	// Trace designates the highest verbosity of log output.
+	Trace = Level{ID: 6, Name: "trace"}
+)