add health command (#2659)

* add health command
* update health check implementation to allow for more checks to added over time
* add change changelog entry

gen/openapiv2/headscale/v1/headscale.swagger.json

@@ -164,6 +164,29 @@
         ]
       }
     },
+    "/api/v1/health": {
+      "get": {
+        "summary": "--- Health start ---",
+        "operationId": "HeadscaleService_Health",
+        "responses": {
+          "200": {
+            "description": "A successful response.",
+            "schema": {
+              "$ref": "#/definitions/v1HealthResponse"
+            }
+          },
+          "default": {
+            "description": "An unexpected error response.",
+            "schema": {
+              "$ref": "#/definitions/rpcStatus"
+            }
+          }
+        },
+        "tags": [
+          "HeadscaleService"
+        ]
+      }
+    },
     "/api/v1/node": {
       "get": {
         "operationId": "HeadscaleService_ListNodes",
@@ -1056,6 +1079,14 @@
         }
       }
     },
+    "v1HealthResponse": {
+      "type": "object",
+      "properties": {
+        "databaseConnectivity": {
+          "type": "boolean"
+        }
+      }
+    },
     "v1ListApiKeysResponse": {
       "type": "object",
       "properties": {