[feature] Add healthcheck endpoints /livez and /readyz (#2783)

* [feature] Add healthcheck endpoints `/livez` and `/readyz`

* use select that returns no data

internal/api/health/ready.go

@@ -0,0 +1,74 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package health
+
+import (
+	"net/http"
+
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+
+	"github.com/gin-gonic/gin"
+)
+
+func (m *Module) ready(c *gin.Context) {
+	if err := m.readyF(c.Request.Context()); err != nil {
+		// Set error on the gin context so
+		// it's logged by the logging middleware.
+		errWithCode := gtserror.NewErrorInternalError(err)
+		c.Error(errWithCode) //nolint:errcheck
+		c.Status(http.StatusInternalServerError)
+	} else {
+		c.Status(http.StatusOK)
+	}
+}
+
+// ReadyGETRequest swagger:operation GET /readyz readyGet
+//
+// Returns code 200 with no body if GoToSocial is "ready", ie., able to connect to the database backend and do a simple SELECT.
+//
+// If GtS is not ready, 500 Internal Error will be returned, and an error will be logged (but not returned to the caller, to avoid leaking internals).
+//
+//	---
+//	tags:
+//	- health
+//
+//	responses:
+//		'200':
+//			description: OK
+//		'500':
+//			description: Not ready. Check logs for error message.
+func (m *Module) ReadyGETRequest(c *gin.Context) {
+	m.ready(c)
+}
+
+// ReadyHEADRequest swagger:operation HEAD /readyz readyHead
+//
+// Returns code 200 with no body if GoToSocial is "ready", ie., able to connect to the database backend and do a simple SELECT.
+//
+// If GtS is not ready, 500 Internal Error will be returned, and an error will be logged (but not returned to the caller, to avoid leaking internals).
+//
+//	---
+//	tags:
+//	- health
+//
+//	responses:
+//		'200':
+//			description: OK
+func (m *Module) ReadyHEADRequest(c *gin.Context) {
+	m.ready(c)
+}