Refactor to use urfave/cli/v2 (#25959)

Replace #10912

And there are many new tests to cover the CLI behavior

There were some concerns about the "option order in hook scripts"
(https://github.com/go-gitea/gitea/pull/10912#issuecomment-1137543314),
it's not a problem now. Because the hook script uses `/gitea hook
--config=/app.ini pre-receive` format. The "config" is a global option,
it can appear anywhere.

----

## ⚠️ BREAKING ⚠️

This PR does it best to avoid breaking anything. The major changes are:

* `gitea` itself won't accept web's options: `--install-port` / `--pid`
/ `--port` / `--quiet` / `--verbose` .... They are `web` sub-command's
options.
    * Use `./gitea web --pid ....` instead
* `./gitea` can still run the `web` sub-command as shorthand, with
default options
* The sub-command's options must follow the sub-command
* Before: `./gitea --sub-opt subcmd` might equal to `./gitea subcmd
--sub-opt` (well, might not ...)
    * After: only `./gitea subcmd --sub-opt` could be used
    * The global options like `--config` are not affected

cmd/cert.go

@@ -20,43 +20,43 @@ import (
 	"strings"
 	"time"
 
-	"github.com/urfave/cli"
+	"github.com/urfave/cli/v2"
 )
 
 // CmdCert represents the available cert sub-command.
-var CmdCert = cli.Command{
+var CmdCert = &cli.Command{
 	Name:  "cert",
 	Usage: "Generate self-signed certificate",
 	Description: `Generate a self-signed X.509 certificate for a TLS server.
 Outputs to 'cert.pem' and 'key.pem' and will overwrite existing files.`,
 	Action: runCert,
 	Flags: []cli.Flag{
-		cli.StringFlag{
+		&cli.StringFlag{
 			Name:  "host",
 			Value: "",
 			Usage: "Comma-separated hostnames and IPs to generate a certificate for",
 		},
-		cli.StringFlag{
+		&cli.StringFlag{
 			Name:  "ecdsa-curve",
 			Value: "",
 			Usage: "ECDSA curve to use to generate a key. Valid values are P224, P256, P384, P521",
 		},
-		cli.IntFlag{
+		&cli.IntFlag{
 			Name:  "rsa-bits",
 			Value: 2048,
 			Usage: "Size of RSA key to generate. Ignored if --ecdsa-curve is set",
 		},
-		cli.StringFlag{
+		&cli.StringFlag{
 			Name:  "start-date",
 			Value: "",
 			Usage: "Creation date formatted as Jan 1 15:04:05 2011",
 		},
-		cli.DurationFlag{
+		&cli.DurationFlag{
 			Name:  "duration",
 			Value: 365 * 24 * time.Hour,
 			Usage: "Duration that certificate is valid for",
 		},
-		cli.BoolFlag{
+		&cli.BoolFlag{
 			Name:  "ca",
 			Usage: "whether this cert should be its own Certificate Authority",
 		},