[feature] Client API endpoints + v. basic web view for pinned posts (#1547)

* implement status pin client api + web handler

* make test names + comments more descriptive

* don't use separate table for status pins

* remove unused add + remove checking

* tidy up + add some more tests

internal/db/bundb/migrations/20230221150957_status_pin_client_api.go

@@ -0,0 +1,65 @@
+/*
+   GoToSocial
+   Copyright (C) 2021-2023 GoToSocial Authors admin@gotosocial.org
+
+   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 migrations
+
+import (
+	"context"
+	"strings"
+
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+	"github.com/uptrace/bun"
+)
+
+func init() {
+	up := func(ctx context.Context, db *bun.DB) error {
+		return db.RunInTx(ctx, nil, func(ctx context.Context, tx bun.Tx) error {
+			// Drop the now unused 'pinned' column in statuses.
+			if _, err := tx.ExecContext(ctx, "ALTER TABLE ? DROP COLUMN ?", bun.Ident("statuses"), bun.Ident("pinned")); err != nil &&
+				!(strings.Contains(err.Error(), "no such column") || strings.Contains(err.Error(), "does not exist") || strings.Contains(err.Error(), "SQLSTATE 42703")) {
+				return err
+			}
+
+			// Create new (more useful) pinned_at column.
+			if _, err := tx.NewAddColumn().Model(&gtsmodel.Status{}).ColumnExpr("? TIMESTAMPTZ", bun.Ident("pinned_at")).Exec(ctx); err != nil &&
+				!(strings.Contains(err.Error(), "already exists") || strings.Contains(err.Error(), "duplicate column name") || strings.Contains(err.Error(), "SQLSTATE 42701")) {
+				return err
+			}
+
+			// Index new column appropriately.
+			if _, err := tx.
+				NewCreateIndex().
+				Model(&gtsmodel.Status{}).
+				Index("statuses_account_id_pinned_at_idx").
+				Column("account_id", "pinned_at").
+				Exec(ctx); err != nil {
+				return err
+			}
+
+			return nil
+		})
+	}
+
+	down := func(ctx context.Context, db *bun.DB) error {
+		return nil
+	}
+
+	if err := Migrations.Register(up, down); err != nil {
+		panic(err)
+	}
+}