build: update logging statements to make json log work - fixes #6038

This changes log statements from log to fs package, which is required for --use-json-log
to properly make log output in JSON format. The recently added custom linting rule,
handled by ruleguard via gocritic via golangci-lint, warns about these and suggests
the alternative. Fixing was therefore basically running "golangci-lint run --fix",
although some manual fixup of mainly imports are necessary following that.

fs/rc/rcserver/rcserver.go

@@ -7,7 +7,6 @@ import (
 	"encoding/json"
 	"flag"
 	"fmt"
-	"log"
 	"mime"
 	"net/http"
 	"net/url"
@@ -86,7 +85,7 @@ func newServer(ctx context.Context, opt *rc.Options, mux *http.ServeMux) (*Serve
 			if opt.Auth.BasicPass == "" && opt.Auth.HtPasswd == "" {
 				randomPass, err := random.Password(128)
 				if err != nil {
-					log.Fatalf("Failed to make password: %v", err)
+					fs.Fatalf(nil, "Failed to make password: %v", err)
 				}
 				opt.Auth.BasicPass = randomPass
 				fs.Infof(nil, "No password specified. Using random password: %s \n", randomPass)