log: Make sink logs encodable (#5441)

* log: make `sink` encodable

* deduplicate logger fields

* extract common fields into `BaseLog` and embed it into `SinkLog`

* amend godoc on `BaseLog` and `SinkLog`

* minor style change

---------

Co-authored-by: Francis Lavoie <lavofr@gmail.com>

modules/caddyhttp/fileserver/command.go

@@ -134,7 +134,9 @@ func cmdFileServer(fs caddycmd.Flags) (int, error) {
 	if debug {
 		cfg.Logging = &caddy.Logging{
 			Logs: map[string]*caddy.CustomLog{
-				"default": {Level: zap.DebugLevel.CapitalString()},
+				"default": {
+					BaseLog: caddy.BaseLog{Level: zap.DebugLevel.CapitalString()},
+				},
 			},
 		}
 	}

modules/caddyhttp/reverseproxy/command.go

@@ -280,7 +280,7 @@ func cmdReverseProxy(fs caddycmd.Flags) (int, error) {
 	if debug {
 		cfg.Logging = &caddy.Logging{
 			Logs: map[string]*caddy.CustomLog{
-				"default": {Level: zap.DebugLevel.CapitalString()},
+				"default": {BaseLog: caddy.BaseLog{Level: zap.DebugLevel.CapitalString()}},
 			},
 		}
 	}

modules/caddyhttp/staticresp.go

@@ -407,7 +407,7 @@ func cmdRespond(fl caddycmd.Flags) (int, error) {
 	if debug {
 		cfg.Logging = &caddy.Logging{
 			Logs: map[string]*caddy.CustomLog{
-				"default": {Level: zap.DebugLevel.CapitalString()},
+				"default": {BaseLog: caddy.BaseLog{Level: zap.DebugLevel.CapitalString()}},
 			},
 		}
 	}