Refactor to use urfave/cli/v2

[wxiaoguang]

Replace #10912

And there are many new tests to cover the CLI behavior

There were some concerns about the "option order in hook scripts" (#10912 (comment)), 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 its 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

[delvh]

Wait, didn't the defaults change in this file?

[wxiaoguang]

What default?

[delvh]

If I'm not mistaken, BoolT returned true when no value has been set, correct?

[wxiaoguang]

In "v1", there are some buggy behaviors. In "v2", no problem:

package main

import (
	"fmt"
	"github.com/urfave/cli/v2"
)

func main() {
	app := cli.NewApp()
	app.Flags = []cli.Flag{
		&cli.BoolFlag{
			Name: "b",
		},
	}
	app.Action = func(ctx *cli.Context) error {
		fmt.Printf("b: %v\n", ctx.Bool("b"))
		return nil
	}
	_ = app.Run([]string{"test", "-b"})
}

Output: b: true

Update: I made a mistake here. Fixed by following PRs.