Do not prepare oauth2 config if it is not enabled, do not write config in some sub-commands (#25567) (#25576)

Backport #25567

Ref:

* https://github.com/go-gitea/gitea/issues/25377#issuecomment-1609757289

And some sub-commands like "generate" / "docs", they do not need to use
the ini config

cmd/embedded.go

@@ -22,9 +22,9 @@ import (
 	"github.com/urfave/cli"
 )
 
-// Cmdembedded represents the available extract sub-command.
+// CmdEmbedded represents the available extract sub-command.
 var (
-	Cmdembedded = cli.Command{
+	CmdEmbedded = cli.Command{
 		Name:        "embedded",
 		Usage:       "Extract embedded resources",
 		Description: "A command for extracting embedded resources, like templates and images",