Add API for License templates (#23009)

This adds a API for getting License templates. This tries to be as close
to the [GitHub
API](https://docs.github.com/en/rest/licenses?apiVersion=2022-11-28) as
possible, but Gitea does not support all features that GitHub has. I
think they should been added, but this out f the scope of this PR. You
should merge #23006 before this PR for security reasons.

templates/swagger/v1_json.tmpl

@@ -883,6 +883,52 @@
         }
       }
     },
+    "/licenses": {
+      "get": {
+        "produces": [
+          "application/json"
+        ],
+        "tags": [
+          "miscellaneous"
+        ],
+        "summary": "Returns a list of all license templates",
+        "operationId": "listLicenseTemplates",
+        "responses": {
+          "200": {
+            "$ref": "#/responses/LicenseTemplateList"
+          }
+        }
+      }
+    },
+    "/licenses/{name}": {
+      "get": {
+        "produces": [
+          "application/json"
+        ],
+        "tags": [
+          "miscellaneous"
+        ],
+        "summary": "Returns information about a license template",
+        "operationId": "getLicenseTemplateInfo",
+        "parameters": [
+          {
+            "type": "string",
+            "description": "name of the license",
+            "name": "name",
+            "in": "path",
+            "required": true
+          }
+        ],
+        "responses": {
+          "200": {
+            "$ref": "#/responses/LicenseTemplateInfo"
+          },
+          "404": {
+            "$ref": "#/responses/notFound"
+          }
+        }
+      }
+    },
     "/markdown": {
       "post": {
         "consumes": [
@@ -18704,6 +18750,52 @@
       },
       "x-go-package": "code.gitea.io/gitea/modules/structs"
     },
+    "LicenseTemplateInfo": {
+      "description": "LicensesInfo contains information about a License",
+      "type": "object",
+      "properties": {
+        "body": {
+          "type": "string",
+          "x-go-name": "Body"
+        },
+        "implementation": {
+          "type": "string",
+          "x-go-name": "Implementation"
+        },
+        "key": {
+          "type": "string",
+          "x-go-name": "Key"
+        },
+        "name": {
+          "type": "string",
+          "x-go-name": "Name"
+        },
+        "url": {
+          "type": "string",
+          "x-go-name": "URL"
+        }
+      },
+      "x-go-package": "code.gitea.io/gitea/modules/structs"
+    },
+    "LicensesTemplateListEntry": {
+      "description": "LicensesListEntry is used for the API",
+      "type": "object",
+      "properties": {
+        "key": {
+          "type": "string",
+          "x-go-name": "Key"
+        },
+        "name": {
+          "type": "string",
+          "x-go-name": "Name"
+        },
+        "url": {
+          "type": "string",
+          "x-go-name": "URL"
+        }
+      },
+      "x-go-package": "code.gitea.io/gitea/modules/structs"
+    },
     "MarkdownOption": {
       "description": "MarkdownOption markdown options",
       "type": "object",
@@ -21587,6 +21679,21 @@
         }
       }
     },
+    "LicenseTemplateInfo": {
+      "description": "LicenseTemplateInfo",
+      "schema": {
+        "$ref": "#/definitions/LicenseTemplateInfo"
+      }
+    },
+    "LicenseTemplateList": {
+      "description": "LicenseTemplateList",
+      "schema": {
+        "type": "array",
+        "items": {
+          "$ref": "#/definitions/LicensesTemplateListEntry"
+        }
+      }
+    },
     "MarkdownRender": {
       "description": "MarkdownRender is a rendered markdown document",
       "schema": {