[API] Add delete release by tag & fix unreleased inconsistency (#14563)

* DeleteReleaseByTag delete release not git tags

* Add api to delete tag (without release)

* fix & extend tests

* fix swagger doc

templates/swagger/v1_json.tmpl

@@ -7964,7 +7964,7 @@
           "repository"
         ],
         "summary": "Get a release by tag name",
-        "operationId": "repoGetReleaseTag",
+        "operationId": "repoGetReleaseByTag",
         "parameters": [
           {
             "type": "string",
@@ -7982,7 +7982,7 @@
           },
           {
             "type": "string",
-            "description": "tagname of the release to get",
+            "description": "tag name of the release to get",
             "name": "tag",
             "in": "path",
             "required": true
@@ -8001,8 +8001,8 @@
         "tags": [
           "repository"
         ],
-        "summary": "Delete a release tag",
-        "operationId": "repoDeleteReleaseTag",
+        "summary": "Delete a release by tag name",
+        "operationId": "repoDeleteReleaseByTag",
         "parameters": [
           {
             "type": "string",
@@ -8020,7 +8020,7 @@
           },
           {
             "type": "string",
-            "description": "name of the tag to delete",
+            "description": "tag name of the release to delete",
             "name": "tag",
             "in": "path",
             "required": true
@@ -8032,9 +8032,6 @@
           },
           "404": {
             "$ref": "#/responses/notFound"
-          },
-          "409": {
-            "$ref": "#/responses/conflict"
           }
         }
       }
@@ -8815,6 +8812,52 @@
         }
       }
     },
+    "/repos/{owner}/{repo}/tags/{tag}": {
+      "delete": {
+        "produces": [
+          "application/json"
+        ],
+        "tags": [
+          "repository"
+        ],
+        "summary": "Delete a repository's tag by name",
+        "operationId": "repoDeleteTag",
+        "parameters": [
+          {
+            "type": "string",
+            "description": "owner of the repo",
+            "name": "owner",
+            "in": "path",
+            "required": true
+          },
+          {
+            "type": "string",
+            "description": "name of the repo",
+            "name": "repo",
+            "in": "path",
+            "required": true
+          },
+          {
+            "type": "string",
+            "description": "name of tag to delete",
+            "name": "tag",
+            "in": "path",
+            "required": true
+          }
+        ],
+        "responses": {
+          "204": {
+            "$ref": "#/responses/empty"
+          },
+          "404": {
+            "$ref": "#/responses/notFound"
+          },
+          "409": {
+            "$ref": "#/responses/conflict"
+          }
+        }
+      }
+    },
     "/repos/{owner}/{repo}/teams": {
       "get": {
         "produces": [