Support repo license (#24872)

Close #278
Close #24076

## Solutions:
- Use
[google/licenseclassifier](https://github.com/google/licenseclassifier/)
Test result between
[google/licensecheck](https://github.com/google/licensecheck) and
[go-license-detector](https://github.com/go-enry/go-license-detector):
https://github.com/go-gitea/gitea/pull/24872#issuecomment-1560361167
Test result between
[google/licensecheck](https://github.com/google/licensecheck) and
[google/licenseclassifier](https://github.com/google/licenseclassifier/):
https://github.com/go-gitea/gitea/pull/24872#issuecomment-1576092178
- Generate License Convert Name List to avoid import license templates
with same contents
Gitea automatically get latest license data from[
spdx/license-list-data](https://github.com/spdx/license-list-data).
But unfortunately, some license templates have same contents. #20915
[click here to see the
list](https://github.com/go-gitea/gitea/pull/24872#issuecomment-1584141684)
So we will generate a list of these license templates with same contents
and create a new file to save the result when using `make
generate-license`. (Need to decide the save path)
- Save License info into a new table `repo_license`
Can easily support searching repo by license in the future.

## Screen shot
Single License:

![image](https://github.com/go-gitea/gitea/assets/18380374/41260bd7-0b4c-4038-8592-508706cffa9f)

Multiple Licenses:

![image](https://github.com/go-gitea/gitea/assets/18380374/34ce2f73-7e18-446b-9b96-ecc4fb61bd70)

Triggers:
- [x] Push commit to default branch
- [x] Create repo
- [x] Mirror repo
- [x] When Default Branch is changed, licenses should be updated

Todo:
- [x] Save Licenses info in to DB when there's a change to license file
in the commit
- [x] DB Migration
- [x] A nominal test?
- [x] Select which library to
use(https://github.com/go-gitea/gitea/pull/24872#issuecomment-1560361167)
- [x] API Support
- [x] Add repo license table
- ~Select license in settings if there are several licenses(Not
recommended)~
- License board(later, not in this PR)

![image](https://github.com/go-gitea/gitea/assets/18380374/2c3c3bf8-bcc2-4c6d-8ce0-81d1a9733878)

---------

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Denys Konovalov <kontakt@denyskon.de>
Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: KN4CK3R <admin@oldschoolhack.me>
Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: 6543 <m.huber@kithara.com>
Co-authored-by: a1012112796 <1012112796@qq.com>
Co-authored-by: techknowlogick <techknowlogick@gitea.com>

build/license/aliasgenerator.go

@@ -0,0 +1,41 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package license
+
+import "strings"
+
+func GetLicenseNameFromAliases(fnl []string) string {
+	if len(fnl) == 0 {
+		return ""
+	}
+
+	shortestItem := func(list []string) string {
+		s := list[0]
+		for _, l := range list[1:] {
+			if len(l) < len(s) {
+				s = l
+			}
+		}
+		return s
+	}
+	allHasPrefix := func(list []string, s string) bool {
+		for _, l := range list {
+			if !strings.HasPrefix(l, s) {
+				return false
+			}
+		}
+		return true
+	}
+
+	sl := shortestItem(fnl)
+	slv := strings.Split(sl, "-")
+	var result string
+	for i := len(slv); i >= 0; i-- {
+		result = strings.Join(slv[:i], "-")
+		if allHasPrefix(fnl, result) {
+			return result
+		}
+	}
+	return ""
+}

build/license/aliasgenerator_test.go

@@ -0,0 +1,39 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package license
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestGetLicenseNameFromAliases(t *testing.T) {
+	tests := []struct {
+		target string
+		inputs []string
+	}{
+		{
+			// real case which you can find in license-aliases.json
+			target: "AGPL-1.0",
+			inputs: []string{
+				"AGPL-1.0-only",
+				"AGPL-1.0-or-late",
+			},
+		},
+		{
+			target: "",
+			inputs: []string{
+				"APSL-1.0",
+				"AGPL-1.0-only",
+				"AGPL-1.0-or-late",
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		result := GetLicenseNameFromAliases(tt.inputs)
+		assert.Equal(t, result, tt.target)
+	}
+}